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Primary Maths · Year 4Chapter 8 · Time
Year 4 · Telling the Time and the 24-Hour Clock · Lesson 8.3

Year 4: Digital time: am, pm and the 24-hour clock

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)

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8.3

Digital time: am, pm and the 24-hour clock

Year 4
Digital 12-hour time with am and pm, 24-hour time, Convert between analogue, 12-hour and 24-hour

A digital clock shows the time in numbers: the hour, a colon (:), then the minutes. A quarter past 3 is 3:15. The minutes always have two digits, so 5 minutes past 3 is 3:05.

A day has 24 hours, but a clock face only has 12. So each time on the clock happens twice every day. We use am and pm to tell them apart.

am (morning)pm (afternoon and evening)12 am00:003 am03:006 am06:009 am09:0012 pm12:003 pm15:006 pm18:009 pm21:0012 am00:00midnightnoon (midday)midnight
One whole day. The 12-hour clock restarts at 12 noon. The 24-hour clock keeps counting up to 24:00.
7:45am7:45pm
07:4519:45
Top: the same two times on a 12-hour display (7:45 am and 7:45 pm). Bottom: on a 24-hour display (07:45 and 19:45).

The 24-hour clock does not need am or pm. It counts the hours from 00 to 23 and always shows four digits: two for the hour and two for the minutes.

12-hour (morning)24-hour12-hour (afternoon)24-hour
12 am00:0012 pm12:00
1 am01:001 pm13:00
2 am02:002 pm14:00
3 am03:003 pm15:00
4 am04:004 pm16:00
5 am05:005 pm17:00
6 am06:006 pm18:00
7 am07:007 pm19:00
8 am08:008 pm20:00
9 am09:009 pm21:00
10 am10:0010 pm22:00
11 am11:0011 pm23:00
Every hour in the 12-hour and 24-hour clocks.

To go the other way, from 24-hour to 12-hour: if the hour is 13 or more, take away 12 and write pm. 21:40 is 21 − 12 = 9, so 9:40 pm.

Key ideas

  • am = morning (midnight to noon). pm = afternoon and evening (noon to midnight).
  • A digital time is the hour, a colon, then the minutes. The minutes always have two digits (3:05).
  • 24-hour clock: no am or pm. It goes from 00:00 to 23:59 and always has four digits.
  • 12-hour to 24-hour: am keeps the hour; pm adds 12.
  • 24-hour to 12-hour: if the hour is 13 or more, take away 12 and write pm.
  • Special times: 12:00 pm is noon (12:00). 12:00 am is midnight (00:00). 12:30 pm is 12:30 but 12:30 am is 00:30.
Worked example 8.3.1
Jack wakes up at half past seven in the morning. Write the time as a digital time with am or pm.

Key words. A digital clock shows the time in numbers: hours, a colon, then minutes (7:45). am is for times between midnight and noon (the morning). pm is for times between noon and midnight (the afternoon and evening). The 24-hour clock counts the hours from 00 to 23 and does not use am or pm.

Method. am is for times from midnight to noon. pm is for times from noon to midnight. Use the clue to choose.

  1. Look at the clue: “in the morning”. It tells us the part of the day.
    Morning: am.   Afternoon or evening: pm.
  2. Choose am or pm. am is for the morning, from midnight until noon.
    in the morning → am
  3. Write the time. Hour, colon, minutes, then am or pm.
    7:30 am

Check. Say it back: 7:30 am is in the morning. ✓

Watch out. 12 noon is 12:00 pm. Midnight is 12:00 am.

Worked example 8.3.2
Amira has her tea at quarter past six in the evening. Write the time as a digital time with am or pm.

Key words. A digital clock shows the time in numbers: hours, a colon, then minutes (7:45). am is for times between midnight and noon (the morning). pm is for times between noon and midnight (the afternoon and evening). The 24-hour clock counts the hours from 00 to 23 and does not use am or pm.

Method. am is for times from midnight to noon. pm is for times from noon to midnight. Use the clue to choose.

  1. Look at the clue: “in the evening”. It tells us the part of the day.
    Morning: am.   Afternoon or evening: pm.
  2. Choose am or pm. pm is for the afternoon and evening, from noon until midnight.
    in the evening → pm
  3. Write the time. Hour, colon, minutes, then am or pm.
    6:15 pm

Check. Say it back: 6:15 pm is in the evening. ✓

Watch out. 12 noon is 12:00 pm. Midnight is 12:00 am.

Worked example 8.3.3
Write 4:25 pm as a 24-hour time.

Key words. A digital clock shows the time in numbers: hours, a colon, then minutes (7:45). am is for times between midnight and noon (the morning). pm is for times between noon and midnight (the afternoon and evening). The 24-hour clock counts the hours from 00 to 23 and does not use am or pm.

Method. For am times the hour stays the same (12 am becomes 00). For pm times add 12 to the hour (12 pm stays 12).

  1. Look at am or pm: 4:25 pm. This tells us which rule to use.
    4:25 pm
  2. Add 12 to the hour. For pm times the 24-hour clock carries on counting after 12.
    4 + 12 = 16
  3. Write the 24-hour time. Two digits for the hour, a colon, two digits for the minutes.
    16:25

Check. Change back: 16:25 is 4:25 pm. ✓

Watch out. Do not add 12 to a morning time, and do not add 12 to 12 pm.

Worked example 8.3.4
Write 8:05 am as a 24-hour time.

Key words. A digital clock shows the time in numbers: hours, a colon, then minutes (7:45). am is for times between midnight and noon (the morning). pm is for times between noon and midnight (the afternoon and evening). The 24-hour clock counts the hours from 00 to 23 and does not use am or pm.

Method. For am times the hour stays the same (12 am becomes 00). For pm times add 12 to the hour (12 pm stays 12).

  1. Look at am or pm: 8:05 am. This tells us which rule to use.
    8:05 am
  2. Keep the hour. For am times the hour number stays the same on the 24-hour clock.
    8 stays 8. Write it with two digits: 08
  3. Write the 24-hour time. Two digits for the hour, a colon, two digits for the minutes.
    08:05

Check. Change back: 08:05 is 8:05 am. ✓

Watch out. Do not add 12 to a morning time, and do not add 12 to 12 pm.

Worked example 8.3.5
Write 21:40 as a 12-hour time with am or pm.

Key words. A digital clock shows the time in numbers: hours, a colon, then minutes (7:45). am is for times between midnight and noon (the morning). pm is for times between noon and midnight (the afternoon and evening). The 24-hour clock counts the hours from 00 to 23 and does not use am or pm.

Method. Before 12:00 it is am and the hour stays. From 13:00 take 12 away and use pm.

  1. Look at the hour in 21:40. It tells us whether it is morning or afternoon.
    The hour is 21.
  2. Take 12 away from the hour. After 12:00 the 24-hour clock goes 13, 14, 15... and the 12-hour clock goes 1, 2, 3... with pm.
    21 − 12 = 9 pm
  3. Write the 12-hour time. Use the colon and the minutes, then am or pm.
    9:40 pm

Check. Change back: 9:40 pm is 21:40. ✓

Watch out. Midnight is 00:00. 24:00 is the same moment at the end of the day.

Worked example 8.3.6
Write 12:15 pm (just after noon) as a 24-hour time.

Key words. A digital clock shows the time in numbers: hours, a colon, then minutes (7:45). am is for times between midnight and noon (the morning). pm is for times between noon and midnight (the afternoon and evening). The 24-hour clock counts the hours from 00 to 23 and does not use am or pm.

Method. For am times the hour stays the same (12 am becomes 00). For pm times add 12 to the hour (12 pm stays 12).

  1. Look at am or pm: 12:15 pm. This tells us which rule to use.
    12:15 pm
  2. Keep the hour. 12:xx pm is just after noon. The hour is still 12.
    12 stays 12
  3. Write the 24-hour time. Two digits for the hour, a colon, two digits for the minutes.
    12:15

Check. Change back: 12:15 is 12:15 pm. ✓

Watch out. Do not add 12 to a morning time, and do not add 12 to 12 pm.

Worked example 8.3.7
Write 00:50 as a 12-hour time with am or pm.

Key words. A digital clock shows the time in numbers: hours, a colon, then minutes (7:45). am is for times between midnight and noon (the morning). pm is for times between noon and midnight (the afternoon and evening). The 24-hour clock counts the hours from 00 to 23 and does not use am or pm.

Method. Before 12:00 it is am and the hour stays. From 13:00 take 12 away and use pm.

  1. Look at the hour in 00:50. It tells us whether it is morning or afternoon.
    The hour is 0.
  2. Change the hour. 00 is just after midnight. On the 12-hour clock we say 12, and it is am.
    00 → 12 am
  3. Write the 12-hour time. Use the colon and the minutes, then am or pm.
    12:50 am

Check. Change back: 12:50 am is 00:50. ✓

Watch out. Midnight is 00:00. 24:00 is the same moment at the end of the day.

Worked example 8.3.8
The clock shows the time on a Saturday afternoon. Write the time as a 24-hour time.
123456789101112

Key words. A digital clock shows the time in numbers: hours, a colon, then minutes (7:45). am is for times between midnight and noon (the morning). pm is for times between noon and midnight (the afternoon and evening). The 24-hour clock counts the hours from 00 to 23 and does not use am or pm.

Method. Read the clock, add am or pm for the part of the day, then (if asked) change it to the 24-hour clock.

  1. Look at the short hand (the hour hand). It tells us the hour. Use the last number it has passed.
    The short hand is between 3 and 4. It has passed 3 but has not reached 4, so the hour is 3.
  2. Look at the long hand (the minute hand). It tells us the minutes. Count in fives from the 12, then count single marks.
    The long hand points at 4. Count in fives: 5, 10, 15, 20.
    4 × 5 = 20 minutes
  3. Read the time in numbers and add am or pm. The question says it is the afternoon or evening, so it is pm.
    3:20 pm = 3:20 pm
  4. Change to the 24-hour clock. am keeps the hour. pm adds 12 (except 12 pm).
    pm: add 12 to the hour. 3 + 12 = 15.
    15:20

Check. 3:20 pm is 15:20 on the 24-hour clock. ✓

Watch out. A clock face cannot tell you am or pm. You need a clue.

Worked example 8.3.9
Which clock shows 15:20? Write the letter.
123456789101112A123456789101112B123456789101112C123456789101112D

Key words. An analogue clock has a round face with two hands. The short, thick hour hand shows the hour. The long, thin minute hand shows the minutes. Past means after the hour. To means before the next hour.

Method. Work out where both hands should be. Then check each clock.

  1. Say the time we want: 15:20 is 12 + 3 = 3 pm, so 3:20 pm. We need the hour and the minutes in numbers.
    3:20
  2. Find where the minute hand should point. The long hand shows the minutes.
    The minute hand points at the 4 (4 × 5 = 20 minutes).
  3. Find where the hour hand should be. The short hand shows the hour.
    The hour hand is between 3 and 4 (it has passed 3).
  4. Check each clock. Read each clock. The right one has both hands in the right places.
    A: shows 3:20 ✓
    B: shows 4:15 × not a match
    C: shows 8:15 × not a match
    D: shows 3:40 × not a match
  5. Choose the clock.
    A

Check. Clock A has the minute hand at 20 minutes and the hour hand past 3. ✓

Watch out. A clock with the hands the wrong way round (short hand for minutes) shows a different time.

Watch out

12 is special. 12:30 pm is not 24:30 and 12:30 am is not 12:30 in the 24-hour clock. At 12 noon the 24-hour hour is 12. Just after midnight it is 00. Also, do not add 12 to a morning time: 4:25 am is 04:25, but 4:25 pm is 16:25.

Exercise 8C  Digital time, am, pm and the 24-hour clock

Non-calculator
1
FWrite each time as a digital time with am or pm.
(a)quarter to eight in the morning before school.
(b)half past three in the afternoon after school.
(c)quarter past eight in the evening at bedtime.
(d)five past eleven in the morning just before lunch.
2
FWrite each time as a 24-hour time.
(a)6:30 am
(b)2:45 pm
(c)9:10 pm
(d)11:55 am
3
FWrite each 24-hour time as a 12-hour time with am or pm.
(a)07:20
(b)13:05
(c)18:45
(d)23:30
4
FThe clocks show the time. Use the clue to write each time as a 12-hour digital time with am or pm.
(a)123456789101112 afternoon
(b)123456789101112 morning
(c)123456789101112 afternoon
(d)123456789101112 evening
5
FThe clocks show the time. Use the clue to write each time as a 24-hour time.
(a)123456789101112 morning
(b)123456789101112 afternoon
(c)123456789101112 night
6
FWhich 24-hour display shows quarter past three in the afternoon? Write the letter.
03:15A15:15B15:45C13:15D
7
FChange each time. Take care with 12.
(a)12:30 pm to a 24-hour time
(b)12:20 am to a 24-hour time
(c)00:05 to a 12-hour time
(d)12:45 to a 12-hour time
8
PSWrite these times in order, earliest first.
7:15 pm    16:50    5:30 pm    18:05
9
PSA shop opens at 09:00 and closes at 17:30. Write both times as 12-hour times.
(a)The shop opens at 09:00.
(b)The shop closes at 17:30.
10
PSRavi’s football training starts at 5:30 pm. Omar’s training starts at 17:15. Whose training starts first? Show how you know.
11
RLeo writes 4:30 pm as 04:30 on the 24-hour clock. What mistake has he made? What should he write?
12
RWhich is the odd one out? Explain.
16:20    4:20 pm    twenty past four in the afternoon    4:20 am
13
RWrite always, sometimes or never for each sentence.
(a)A pm time written on the 24-hour clock has an hour that is 12 more than the 12-hour hour.
(b)A 24-hour time has am or pm after it.
(c)The hour of a 24-hour time is 13 or more.
14
RNoah says, “A 12-hour digital clock shows 12:00 two times every day.” Is he right? Write what the clock shows each time, with am or pm, and the 24-hour time.

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