Year 4: How long does it take? Durations, start times and end times
Part of the Year 4 telling the time and the 24-hour clock chapter. Chapter overview · whole chapter on one page · Download worksheet (PDF) · Answers (PDF)
How long does it take? Durations, start times and end times
The duration of something is how long it takes. To find a duration, we do not take one time away from the other like in a normal subtraction, because there are 60 minutes in an hour. We count on instead, on a number line.
Three easy jumps. Start at the start time.
- Jump to the next o’clock.
- Jump along in whole hours until you reach the hour of the end time.
- Jump the last minutes to the end time.
Add the jumps. Add the hours, then add the minutes. If the minutes come to 60 or more, change 60 minutes into 1 hour.
Finding an end time. If a film starts at 2:25 pm and lasts 1 hour 50 minutes, add the whole hours first (2:25 + 1 hour = 3:25), then count on the minutes through the next o’clock: 3:25 + 35 minutes = 4:00, then 4:00 + 15 minutes = 4:15 pm.
Finding a start time. Count back from the end time. Take away the whole hours first, then the minutes, going back to the o’clock on the way.
Across noon or midnight. The same method works. Count on to 12:00 (noon or midnight), then carry on. The 24-hour clock makes this easier: 22:30 to 06:15 is 22:30 → 24:00 (1 hour 30 minutes) and 00:00 → 06:15 (6 hours 15 minutes).
Key ideas
- Duration = how long something takes. To find it, count on: to the next o’clock, then whole hours, then the last minutes.
- There are 60 minutes in an hour. 3:50 to 4:20 is 30 minutes (10 + 20), not 70.
- End time = start time + duration. Add the whole hours first, then the minutes.
- Start time = end time − duration. Count back the whole hours first, then the minutes.
- Across noon or midnight, count on to 12:00 and then carry on. Pay attention to am and pm.
- Check by counting: start + duration should give the end time.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.3:10 pm to 3:45 pm: 45 − 10 = 35 minutes
- Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 35
Total: 35 minutes
Check. Count on from the start: 3:10 pm + 35 minutes = 3:45 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.4:40 pm to 5:00 pm: 20 minutes to the next o'clock
60 − 40 = 20 minutes
5:00 pm to 5:25 pm: the minutes after the o'clock: 25 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 20 + 25 = 45
Total: 45 minutes
Check. Count on from the start: 4:40 pm + 45 minutes = 5:25 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.9:20 am to 10:00 am: 40 minutes to the next o'clock
60 − 20 = 40 minutes
10:00 am to 12:00 pm: whole hours: 2 hours
12:00 pm to 12:05 pm: the minutes after the o'clock: 5 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 2 hours
Minutes: 40 + 5 = 45
Total: 2 hours 45 minutes
Check. Count on from the start: 9:20 am + 2 hours 45 minutes = 12:05 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Read the first clock. This is the start time.The first clock shows 2:20 (twenty past two).
- Read the second clock. This is the end time.The second clock shows 4:05 (five past four).
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.2:20 to 3:00: 40 minutes to the next o'clock
60 − 20 = 40 minutes
3:00 to 4:00: whole hours: 1 hour
4:00 to 4:05: the minutes after the o'clock: 5 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 1 hour
Minutes: 40 + 5 = 45
Total: 1 hour 45 minutes
Check. Count on from the start: 2:20 + 1 hour 45 minutes = 4:05. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.14:35 to 15:00: 25 minutes to the next o'clock
60 − 35 = 25 minutes
15:00 to 17:00: whole hours: 2 hours
17:00 to 17:10: the minutes after the o'clock: 10 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 2 hours
Minutes: 25 + 10 = 35
Total: 2 hours 35 minutes
Check. Count on from the start: 14:35 + 2 hours 35 minutes = 17:10. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.10:30 pm to 11:00 pm: 30 minutes to the next o'clock
60 − 30 = 30 minutes
11:00 pm to 6:00 am: whole hours: 7 hours
6:00 am to 6:15 am: the minutes after the o'clock: 15 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 7 hours
Minutes: 30 + 15 = 45
Total: 7 hours 45 minutes
Check. Count on from the start: 10:30 pm + 7 hours 45 minutes = 6:15 am. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Add the whole hours first. Then add the minutes, jumping to the next o'clock if you pass it.
- Start at the start time and count on the whole hours first. Adding whole hours is easy: the minutes stay the same.2:25 pm + 1 hour = 3:25 pm
- Count on the 50 minutes. Going to the next o'clock first makes the sum easy. The minutes left are added after.Jump to the next o'clock: 60 − 25 = 35 minutes, so 3:25 pm + 35 min = 4:00 pm.
Jump the rest: 50 − 35 = 15 minutes, so 4:00 pm + 15 min = 4:15 pm - Look at the number line. It shows all the jumps from the start to the end.
- Write the end time. 4:15 pm
Check. Count back from the end: 4:15 pm − 1 hour 50 minutes = 2:25 pm. ✓
Watch out. The minutes go up to 60, then the hour changes. 2:45 + 30 minutes is 3:15, not 2:75.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Add the whole hours first. Then add the minutes, jumping to the next o'clock if you pass it.
- Start at the start time and count on the whole hours first. Adding whole hours is easy: the minutes stay the same.15:40 + 2 hours = 17:40
- Count on the 35 minutes. Going to the next o'clock first makes the sum easy. The minutes left are added after.Jump to the next o'clock: 60 − 40 = 20 minutes, so 17:40 + 20 min = 18:00.
Jump the rest: 35 − 20 = 15 minutes, so 18:00 + 15 min = 18:15 - Look at the number line. It shows all the jumps from the start to the end.
- Write the end time. 18:15
Check. Count back from the end: 18:15 − 2 hours 35 minutes = 15:40. ✓
Watch out. The minutes go up to 60, then the hour changes. 2:45 + 30 minutes is 3:15, not 2:75.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count back from the end time: first the whole hours, then the minutes, going through the o'clock if you need to.
- Start at the end time and count back the whole hours first. Taking away whole hours is easy: the minutes stay the same.5:10 pm − 2 hours = 3:10 pm
- Count back the 35 minutes. Going back to the o'clock first makes the sum easy. Then we take away the minutes that are left.Go back to the o'clock first: 3:10 pm − 10 min = 3:00 pm.
Go back the rest: 35 − 10 = 25 minutes, so 3:00 pm − 25 min = 2:35 pm - Look at the number line. The arrows show the jumps back from the end time.
- Write the start time. 2:35 pm
Check. Count on from the start: 2:35 pm + 2 hours 35 minutes = 5:10 pm. ✓
Watch out. When you count back through an o'clock the hour goes down by one. 3:10 minus 20 minutes is 2:50.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count back from the end time: first the whole hours, then the minutes, going through the o'clock if you need to.
- Start at the end time and count back the whole hours first. Taking away whole hours is easy: the minutes stay the same.09:05 − 1 hour = 08:05
- Count back the 30 minutes. Going back to the o'clock first makes the sum easy. Then we take away the minutes that are left.Go back to the o'clock first: 08:05 − 5 min = 08:00.
Go back the rest: 30 − 5 = 25 minutes, so 08:00 − 25 min = 07:35 - Look at the number line. The arrows show the jumps back from the end time.
- Write the start time. 07:35
Check. Count on from the start: 07:35 + 1 hour 30 minutes = 09:05. ✓
Watch out. When you count back through an o'clock the hour goes down by one. 3:10 minus 20 minutes is 2:50.
Watch out
An hour is 60 minutes, not 100. From 3:50 to 5:20 is not “2 hours 30” and the minutes cannot go above 59. 3:50 to 4:00 is 10 minutes, 4:00 to 5:00 is 1 hour, 5:00 to 5:20 is 20 minutes: 1 hour 30 minutes. Also, when you count back through an o’clock, the hour goes down.Exercise 8F Durations, start times and end times
Non-calculatorKey words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.9:10 am to 9:50 am: 50 − 10 = 40 minutes
- Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 40
Total: 40 minutes
Check. Count on from the start: 9:10 am + 40 minutes = 9:50 am. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.3:20 pm to 3:55 pm: 55 − 20 = 35 minutes
- Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 35
Total: 35 minutes
Check. Count on from the start: 3:20 pm + 35 minutes = 3:55 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.11:05 am to 11:50 am: 50 − 5 = 45 minutes
- Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 45
Total: 45 minutes
Check. Count on from the start: 11:05 am + 45 minutes = 11:50 am. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.6:15 pm to 6:45 pm: 45 − 15 = 30 minutes
- Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 30
Total: 30 minutes
Check. Count on from the start: 6:15 pm + 30 minutes = 6:45 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.4:40 pm to 5:00 pm: 20 minutes to the next o'clock
60 − 40 = 20 minutes
5:00 pm to 5:15 pm: the minutes after the o'clock: 15 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 20 + 15 = 35
Total: 35 minutes
Check. Count on from the start: 4:40 pm + 35 minutes = 5:15 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.8:50 am to 9:00 am: 10 minutes to the next o'clock
60 − 50 = 10 minutes
9:00 am to 9:20 am: the minutes after the o'clock: 20 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 10 + 20 = 30
Total: 30 minutes
Check. Count on from the start: 8:50 am + 30 minutes = 9:20 am. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.1:35 pm to 2:00 pm: 25 minutes to the next o'clock
60 − 35 = 25 minutes
2:00 pm to 2:10 pm: the minutes after the o'clock: 10 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 25 + 10 = 35
Total: 35 minutes
Check. Count on from the start: 1:35 pm + 35 minutes = 2:10 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.7:45 pm to 8:00 pm: 15 minutes to the next o'clock
60 − 45 = 15 minutes
8:00 pm to 8:25 pm: the minutes after the o'clock: 25 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 15 + 25 = 40
Total: 40 minutes
Check. Count on from the start: 7:45 pm + 40 minutes = 8:25 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.9:15 am to 10:00 am: 45 minutes to the next o'clock
60 − 15 = 45 minutes
10:00 am to 11:00 am: whole hours: 1 hour
11:00 am to 11:40 am: the minutes after the o'clock: 40 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 1 hour
Minutes: 45 + 40 = 85
85 minutes = 1 hour 25 minutes
Total: 2 hours 25 minutes
Check. Count on from the start: 9:15 am + 2 hours 25 minutes = 11:40 am. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.2:30 pm to 3:00 pm: 30 minutes to the next o'clock
60 − 30 = 30 minutes
3:00 pm to 5:00 pm: whole hours: 2 hours
5:00 pm to 5:10 pm: the minutes after the o'clock: 10 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 2 hours
Minutes: 30 + 10 = 40
Total: 2 hours 40 minutes
Check. Count on from the start: 2:30 pm + 2 hours 40 minutes = 5:10 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.7:20 am to 8:00 am: 40 minutes to the next o'clock
60 − 20 = 40 minutes
8:00 am to 10:00 am: whole hours: 2 hours
10:00 am to 10:05 am: the minutes after the o'clock: 5 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 2 hours
Minutes: 40 + 5 = 45
Total: 2 hours 45 minutes
Check. Count on from the start: 7:20 am + 2 hours 45 minutes = 10:05 am. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.12:45 pm to 1:00 pm: 15 minutes to the next o'clock
60 − 45 = 15 minutes
1:00 pm to 4:00 pm: whole hours: 3 hours
4:00 pm to 4:15 pm: the minutes after the o'clock: 15 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 3 hours
Minutes: 15 + 15 = 30
Total: 3 hours 30 minutes
Check. Count on from the start: 12:45 pm + 3 hours 30 minutes = 4:15 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Read the first clock. This is the start time.The first clock shows 2:10 (ten past two).
- Read the second clock. This is the end time.The second clock shows 3:50 (ten to four).
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.2:10 to 3:00: 50 minutes to the next o'clock
60 − 10 = 50 minutes
3:00 to 3:50: the minutes after the o'clock: 50 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 50 + 50 = 100
100 minutes = 1 hour 40 minutes
Total: 1 hour 40 minutes
Check. Count on from the start: 2:10 + 1 hour 40 minutes = 3:50. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Read the first clock. This is the start time.The first clock shows 5:35 (twenty-five to six).
- Read the second clock. This is the end time.The second clock shows 7:05 (five past seven).
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.5:35 to 6:00: 25 minutes to the next o'clock
60 − 35 = 25 minutes
6:00 to 7:00: whole hours: 1 hour
7:00 to 7:05: the minutes after the o'clock: 5 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 1 hour
Minutes: 25 + 5 = 30
Total: 1 hour 30 minutes
Check. Count on from the start: 5:35 + 1 hour 30 minutes = 7:05. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Read the first clock. This is the start time.The first clock shows 10:20 (twenty past ten).
- Read the second clock. This is the end time.The second clock shows 11:55 (five to twelve).
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.10:20 to 11:00: 40 minutes to the next o'clock
60 − 20 = 40 minutes
11:00 to 11:55: the minutes after the o'clock: 55 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 40 + 55 = 95
95 minutes = 1 hour 35 minutes
Total: 1 hour 35 minutes
Check. Count on from the start: 10:20 + 1 hour 35 minutes = 11:55. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Add the whole hours first. Then add the minutes, jumping to the next o'clock if you pass it.
- Start at the start time and count on the whole hours first. There are no whole hours to add.2:20 pm
- Count on the 45 minutes. Going to the next o'clock first makes the sum easy. The minutes left are added after.Jump to the next o'clock: 60 − 20 = 40 minutes, so 2:20 pm + 40 min = 3:00 pm.
Jump the rest: 45 − 40 = 5 minutes, so 3:00 pm + 5 min = 3:05 pm - Look at the number line. It shows all the jumps from the start to the end.
- Write the end time. 3:05 pm
Check. Count back from the end: 3:05 pm − 45 minutes = 2:20 pm. ✓
Watch out. The minutes go up to 60, then the hour changes. 2:45 + 30 minutes is 3:15, not 2:75.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Add the whole hours first. Then add the minutes, jumping to the next o'clock if you pass it.
- Start at the start time and count on the whole hours first. Adding whole hours is easy: the minutes stay the same.10:35 am + 1 hour = 11:35 am
- Count on the 30 minutes. Going to the next o'clock first makes the sum easy. The minutes left are added after.Jump to the next o'clock: 60 − 35 = 25 minutes, so 11:35 am + 25 min = 12:00 pm.
Jump the rest: 30 − 25 = 5 minutes, so 12:00 pm + 5 min = 12:05 pm - Look at the number line. It shows all the jumps from the start to the end.
- Write the end time. 12:05 pm
Check. Count back from the end: 12:05 pm − 1 hour 30 minutes = 10:35 am. ✓
Watch out. The minutes go up to 60, then the hour changes. 2:45 + 30 minutes is 3:15, not 2:75.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Add the whole hours first. Then add the minutes, jumping to the next o'clock if you pass it.
- Start at the start time and count on the whole hours first. Adding whole hours is easy: the minutes stay the same.4:50 pm + 2 hours = 6:50 pm
- Count on the 20 minutes. Going to the next o'clock first makes the sum easy. The minutes left are added after.Jump to the next o'clock: 60 − 50 = 10 minutes, so 6:50 pm + 10 min = 7:00 pm.
Jump the rest: 20 − 10 = 10 minutes, so 7:00 pm + 10 min = 7:10 pm - Look at the number line. It shows all the jumps from the start to the end.
- Write the end time. 7:10 pm
Check. Count back from the end: 7:10 pm − 2 hours 20 minutes = 4:50 pm. ✓
Watch out. The minutes go up to 60, then the hour changes. 2:45 + 30 minutes is 3:15, not 2:75.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Add the whole hours first. Then add the minutes, jumping to the next o'clock if you pass it.
- Start at the start time and count on the whole hours first. Adding whole hours is easy: the minutes stay the same.8:15 am + 3 hours = 11:15 am
- Count on the 50 minutes. Going to the next o'clock first makes the sum easy. The minutes left are added after.Jump to the next o'clock: 60 − 15 = 45 minutes, so 11:15 am + 45 min = 12:00 pm.
Jump the rest: 50 − 45 = 5 minutes, so 12:00 pm + 5 min = 12:05 pm - Look at the number line. It shows all the jumps from the start to the end.
- Write the end time. 12:05 pm
Check. Count back from the end: 12:05 pm − 3 hours 50 minutes = 8:15 am. ✓
Watch out. The minutes go up to 60, then the hour changes. 2:45 + 30 minutes is 3:15, not 2:75.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count back from the end time: first the whole hours, then the minutes, going through the o'clock if you need to.
- Start at the end time and count back the whole hours first. There are no whole hours to take away.4:30 pm
- Count back the 50 minutes. Going back to the o'clock first makes the sum easy. Then we take away the minutes that are left.Go back to the o'clock first: 4:30 pm − 30 min = 4:00 pm.
Go back the rest: 50 − 30 = 20 minutes, so 4:00 pm − 20 min = 3:40 pm - Look at the number line. The arrows show the jumps back from the end time.
- Write the start time. 3:40 pm
Check. Count on from the start: 3:40 pm + 50 minutes = 4:30 pm. ✓
Watch out. When you count back through an o'clock the hour goes down by one. 3:10 minus 20 minutes is 2:50.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count back from the end time: first the whole hours, then the minutes, going through the o'clock if you need to.
- Start at the end time and count back the whole hours first. Taking away whole hours is easy: the minutes stay the same.11:15 am − 1 hour = 10:15 am
- Count back the 45 minutes. Going back to the o'clock first makes the sum easy. Then we take away the minutes that are left.Go back to the o'clock first: 10:15 am − 15 min = 10:00 am.
Go back the rest: 45 − 15 = 30 minutes, so 10:00 am − 30 min = 9:30 am - Look at the number line. The arrows show the jumps back from the end time.
- Write the start time. 9:30 am
Check. Count on from the start: 9:30 am + 1 hour 45 minutes = 11:15 am. ✓
Watch out. When you count back through an o'clock the hour goes down by one. 3:10 minus 20 minutes is 2:50.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count back from the end time: first the whole hours, then the minutes, going through the o'clock if you need to.
- Start at the end time and count back the whole hours first. Taking away whole hours is easy: the minutes stay the same.6:05 pm − 2 hours = 4:05 pm
- Count back the 20 minutes. Going back to the o'clock first makes the sum easy. Then we take away the minutes that are left.Go back to the o'clock first: 4:05 pm − 5 min = 4:00 pm.
Go back the rest: 20 − 5 = 15 minutes, so 4:00 pm − 15 min = 3:45 pm - Look at the number line. The arrows show the jumps back from the end time.
- Write the start time. 3:45 pm
Check. Count on from the start: 3:45 pm + 2 hours 20 minutes = 6:05 pm. ✓
Watch out. When you count back through an o'clock the hour goes down by one. 3:10 minus 20 minutes is 2:50.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count back from the end time: first the whole hours, then the minutes, going through the o'clock if you need to.
- Start at the end time and count back the whole hours first. There are no whole hours to take away.1:10 pm
- Count back the 25 minutes. Going back to the o'clock first makes the sum easy. Then we take away the minutes that are left.Go back to the o'clock first: 1:10 pm − 10 min = 1:00 pm.
Go back the rest: 25 − 10 = 15 minutes, so 1:00 pm − 15 min = 12:45 pm - Look at the number line. The arrows show the jumps back from the end time.
- Write the start time. 12:45 pm
Check. Count on from the start: 12:45 pm + 25 minutes = 1:10 pm. ✓
Watch out. When you count back through an o'clock the hour goes down by one. 3:10 minus 20 minutes is 2:50.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.13:15 to 14:00: 45 minutes to the next o'clock
60 − 15 = 45 minutes
14:00 to 15:00: whole hours: 1 hour
15:00 to 15:50: the minutes after the o'clock: 50 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 1 hour
Minutes: 45 + 50 = 95
95 minutes = 1 hour 35 minutes
Total: 2 hours 35 minutes
Check. Count on from the start: 13:15 + 2 hours 35 minutes = 15:50. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.09:40 to 10:00: 20 minutes to the next o'clock
60 − 40 = 20 minutes
10:00 to 12:00: whole hours: 2 hours
12:00 to 12:10: the minutes after the o'clock: 10 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 2 hours
Minutes: 20 + 10 = 30
Total: 2 hours 30 minutes
Check. Count on from the start: 09:40 + 2 hours 30 minutes = 12:10. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.16:25 to 17:00: 35 minutes to the next o'clock
60 − 25 = 35 minutes
17:00 to 18:00: whole hours: 1 hour
18:00 to 18:05: the minutes after the o'clock: 5 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 1 hour
Minutes: 35 + 5 = 40
Total: 1 hour 40 minutes
Check. Count on from the start: 16:25 + 1 hour 40 minutes = 18:05. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.20:50 to 21:00: 10 minutes to the next o'clock
60 − 50 = 10 minutes
21:00 to 23:00: whole hours: 2 hours
23:00 to 23:20: the minutes after the o'clock: 20 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 2 hours
Minutes: 10 + 20 = 30
Total: 2 hours 30 minutes
Check. Count on from the start: 20:50 + 2 hours 30 minutes = 23:20. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.11:30 am to 12:00 pm: 30 minutes to the next o'clock
60 − 30 = 30 minutes
12:00 pm to 1:00 pm: whole hours: 1 hour
1:00 pm to 1:15 pm: the minutes after the o'clock: 15 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 1 hour
Minutes: 30 + 15 = 45
Total: 1 hour 45 minutes
Check. Count on from the start: 11:30 am + 1 hour 45 minutes = 1:15 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.9:45 pm to 10:00 pm: 15 minutes to the next o'clock
60 − 45 = 15 minutes
10:00 pm to 12:00 am: whole hours: 2 hours
12:00 am to 12:20 am: the minutes after the o'clock: 20 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 2 hours
Minutes: 15 + 20 = 35
Total: 2 hours 35 minutes
Check. Count on from the start: 9:45 pm + 2 hours 35 minutes = 12:20 am. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.10:15 pm to 11:00 pm: 45 minutes to the next o'clock
60 − 15 = 45 minutes
11:00 pm to 6:00 am: whole hours: 7 hours
6:00 am to 6:30 am: the minutes after the o'clock: 30 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 7 hours
Minutes: 45 + 30 = 75
75 minutes = 1 hour 15 minutes
Total: 8 hours 15 minutes
Check. Count on from the start: 10:15 pm + 8 hours 15 minutes = 6:30 am. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. The first jump goes from 3:35 pm to the next o’clock.
- Find the next o’clock. After 3:35 comes 4:00.3:35 to 4:00
- Count the minutes. 60 minutes in an hour.60 − 35 = 25 minutes
Check. 3:35 + 25 minutes = 4:00. ✓
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. The second jump goes from 4:00 pm to 6:00 pm.
- Count the hours. It is a jump of whole hours.4 to 5 is 1 hour, 5 to 6 is 1 hour
- Write the jump. 2 hours
Check. 4:00 + 2 hours = 6:00. ✓
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.3:35 pm to 4:00 pm: 25 minutes to the next o'clock
60 − 35 = 25 minutes
4:00 pm to 6:00 pm: whole hours: 2 hours
6:00 pm to 6:20 pm: the minutes after the o'clock: 20 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 2 hours
Minutes: 25 + 20 = 45
Total: 2 hours 45 minutes
Check. Count on from the start: 3:35 pm + 2 hours 45 minutes = 6:20 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Add the whole hours first. Then add the minutes, jumping to the next o'clock if you pass it.
- Start at the start time and count on the whole hours first. Adding whole hours is easy: the minutes stay the same.3:15 pm + 1 hour = 4:15 pm
- Count on the 45 minutes. The minutes fit inside the hour, so we can add them in one jump.4:15 pm + 45 minutes = 5:00 pm
- Look at the number line. It shows all the jumps from the start to the end.
- Write the end time. 5:00 pm
Check. Count back from the end: 5:00 pm − 1 hour 45 minutes = 3:15 pm. ✓
Watch out. The minutes go up to 60, then the hour changes. 2:45 + 30 minutes is 3:15, not 2:75.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.4:50 pm to 5:00 pm: 10 minutes to the next o'clock
60 − 50 = 10 minutes
5:00 pm to 5:35 pm: the minutes after the o'clock: 35 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 10 + 35 = 45
Total: 45 minutes
Check. Count on from the start: 4:50 pm + 45 minutes = 5:35 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.5:05 pm to 5:55 pm: 55 − 5 = 50 minutes
- Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Minutes: 50
Total: 50 minutes
Check. Count on from the start: 5:05 pm + 50 minutes = 5:55 pm. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Compare the two times. The bigger number of minutes is longer.
- Write the times. We found them in parts (a) and (b).Priya: 45 minutes. Leo: 50 minutes.
- Compare. 50 is more than 45.Leo worked for longer.
- Find how much longer. Take the smaller from the bigger.50 − 45 = 5 minutes
Check. 45 + 5 = 50. ✓
Watch out. Find both times first, then compare.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from the start to the end on a number line: first to the next o'clock, then in whole hours, then the last minutes. Then add the jumps.
- Draw a number line and count on from the start time to the end time. Counting on in easy jumps (first to the next o'clock, then whole hours, then the last minutes) is easier than taking one time away from the other.
- Work out each jump. Each jump is easy to do in your head.7:40 pm to 8:00 pm: 20 minutes to the next o'clock
60 − 40 = 20 minutes
8:00 pm to 6:00 am: whole hours: 10 hours
6:00 am to 6:10 am: the minutes after the o'clock: 10 minutes - Add the jumps. Add the hours together, then add the minutes together. If the minutes reach 60 or more, change 60 minutes into 1 hour.Hours: 10 hours
Minutes: 20 + 10 = 30
Total: 10 hours 30 minutes
Check. Count on from the start: 7:40 pm + 10 hours 30 minutes = 6:10 am. ✓
Watch out. There are 60 minutes in an hour, not 100. 3:50 to 4:20 is 30 minutes, not 70.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count on from 3:50 to 5:20 in the right jumps. Then compare with what Tom said.
- Count on to the next o’clock. From 3:50 to 4:00.10 minutes
- Count whole hours. From 4:00 to 5:00.1 hour
- Count the last minutes. From 5:00 to 5:20.20 minutes
- Add. Hours and minutes: 1 hour and 10 + 20 minutes.1 hour 30 minutes
Check. 3:50 + 1 hour 30 minutes = 5:20. ✓
Watch out. Tom did 5:20 minus 3:50 as if they were normal numbers (520 − 350 = 170). The minutes only go up to 59, and 70 minutes is 1 hour 10 minutes.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Work out when the film finishes. Then compare it with 10 pm.
- Find the end time. Start at 7:45 pm and add 2 hours 20 minutes.7:45 pm + 2 hours = 9:45 pm. 9:45 pm + 15 minutes = 10:00 pm, and 10:00 pm + 5 minutes = 10:05 pm
- Compare with 10 pm. 10:05 pm is later than 10:00 pm.10:05 pm is 5 minutes after 10 pm.
- Answer. Amira is not right. The film finishes at 10:05 pm, after 10 pm.
Check. Count on from 7:45 pm to 10:00 pm = 2 hours 15 minutes, which is less than 2 hours 20 minutes. ✓
Watch out. Count through the o’clock. 9:45 + 20 minutes is 10:05, not 9:65.
Key words. The duration is how long something takes (how much time goes by). To count on is to jump forward from one time to another. The start time is when something begins. The end time is when it finishes.
Method. Count back from the end time: first the whole hours, then the minutes, going through the o'clock if you need to.
- Start at the end time and count back the whole hours first. Taking away whole hours is easy: the minutes stay the same.00:10 − 3 hours = 21:10
- Count back the 45 minutes. Going back to the o'clock first makes the sum easy. Then we take away the minutes that are left.Go back to the o'clock first: 21:10 − 10 min = 21:00.
Go back the rest: 45 − 10 = 35 minutes, so 21:00 − 35 min = 20:25 - Look at the number line. The arrows show the jumps back from the end time.
- Write the start time. 20:25
Check. Count on from the start: 20:25 + 3 hours 45 minutes = 00:10. ✓
Watch out. When you count back through an o'clock the hour goes down by one. 3:10 minus 20 minutes is 2:50.