Measures in context
By the end of this chapter you will be able to
- Change a measure from one unit to another, including decimals
- Work out how long something takes from a start and an end time
- Use an approximate conversion between miles and kilometres, or pounds and kilograms
- Find the area of a rectangle, a triangle or a parallelogram, and of a shape made of rectangles
- Explain why two shapes with the same area can have different perimeters
You should already know
- Metric units and the four operations with decimals (Year 5 measures)
- Area of a rectangle and the times tables (Year 5 measures)
Where this leads
- Position and coordinates (Chapter 6 of this book)
KS2 SATs practice for reasoning (Year 6). Original questions in the style of the national tests. Content: Convert between metric units of length, mass and capacity, including decimals (Year 5-6), Use, read, write and convert between standard units, using decimal notation (Year 6), Convert between miles and kilometres, and use approximate imperial equivalents (Year 5-6), Solve problems involving the calculation and conversion of units of measure (Year 6), Convert between units of time, including timetables and durations (Year 5-6), Calculate the perimeter of composite rectilinear shapes and the area of rectangles, triangles and parallelograms (Year 5-6), Recognise that shapes with the same area can have different perimeters, and compare the volumes of cubes and cuboids (Year 6).
Exercise P Do you remember?
Non-calculatorMethod. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many cm make one m. There are 100 cm in 1 m.1 m = 100 cm
- Multiply by 100. Changing to a smaller unit needs more of them, so the number gets bigger: multiply.3 x 100 = 300
- Write the answer with the new unit. Keep the same measure, in the new unit.300 cm
- Write the answer. 300 cm
Check. 300 cm is the same length, mass or volume as 3 m. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. One hour has 60 minutes.
- Multiply. 2 x 60 = 120.120
- Write the answer. 120
Check. 120 / 60 = 2. ✓
Method. Multiply the length by the width.
- Write the formula. Area of a rectangle = length x width.5 x 4
- Multiply. Multiply the length by the width.5 x 4 = 20
- Write the units as square units. The area is measured in square cm.20 cm²
- Write the answer. 20 cm²
Check. 20 / 5 = 4. ✓
Watch out. Area is measured in square units, so the answer ends with a small 2, such as cm².
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many g make one kg. There are 1000 g in 1 kg.1 kg = 1000 g
- Multiply by 1000. Changing to a smaller unit needs more of them, so the number gets bigger: multiply.0.5 x 1000 = 500
- Write the answer with the new unit. Keep the same measure, in the new unit.500 g
- Write the answer. 500 g
Check. 500 g is the same length, mass or volume as 0.5 kg. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. One metre is 100 cm.
- Multiply. 0.4 x 100 = 40.40 cm
- Write the answer. 40 cm
Check. 40 / 100 = 0.4. ✓
Metric units of length, mass and capacity
Rule
Length: 10 mm = 1 cm, 100 cm = 1 m, 1000 m = 1 km. Mass: 1000 g = 1 kg. Capacity: 1000 ml = 1 litre.
Changing to a smaller unit gives a bigger number: multiply. Changing to a bigger unit gives a smaller number: divide.
Key ideas
- Smaller unit: multiply. Bigger unit: divide.
- 1 kg = 1000 g, so 2.5 kg = 2500 g.
- Check the answer: a bigger unit should give a smaller number.
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many m make one km. There are 1000 m in 1 km.1 km = 1000 m
- Multiply by 1000. Changing to a smaller unit needs more of them, so the number gets bigger: multiply.2.5 x 1000 = 2500
- Write the answer with the new unit. Keep the same measure, in the new unit.2500 m
- Write the answer. 2500 m
Check. 2500 m is the same length, mass or volume as 2.5 km. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many g make one kg. There are 1000 g in 1 kg.1 kg = 1000 g
- Divide by 1000. Changing to a bigger unit needs fewer of them, so the number gets smaller: divide.4500 / 1000 = 4.5
- Write the answer with the new unit. Keep the same measure, in the new unit.4.5 kg
- Write the answer. 4.5 kg
Check. 4.5 kg is the same length, mass or volume as 4500 g. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many ml make one l. There are 1000 ml in 1 l.1 l = 1000 ml
- Multiply by 1000. Changing to a smaller unit needs more of them, so the number gets bigger: multiply.0.75 x 1000 = 750
- Write the answer with the new unit. Keep the same measure, in the new unit.750 ml
- Write the answer. 750 ml
Check. 750 ml is the same length, mass or volume as 0.75 l. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Watch out
Watch out. 0.5 km is 500 m, not 50 m. Move the decimal point the right number of places.
Exam tip
Practice guide. Write both units in the question first, then decide whether to multiply or divide.
Exercise 4A Practice: metric units
Non-calculatorMethod. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many cm make one m. There are 100 cm in 1 m.1 m = 100 cm
- Multiply by 100. Changing to a smaller unit needs more of them, so the number gets bigger: multiply.1.199999999999999955591079015 x 100 = 119.9999999999999955591079015
- Write the answer with the new unit. Keep the same measure, in the new unit.119.9999999999999955591079015 cm
- Write the answer. 119.9999999999999955591079015 cm
Check. 119.9999999999999955591079015 cm is the same length, mass or volume as 1.199999999999999955591079015 m. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many ml make one l. There are 1000 ml in 1 l.1 l = 1000 ml
- Divide by 1000. Changing to a bigger unit needs fewer of them, so the number gets smaller: divide.3500 / 1000 = 3.5
- Write the answer with the new unit. Keep the same measure, in the new unit.3.5 l
- Write the answer. 3.5 l
Check. 3.5 l is the same length, mass or volume as 3500 ml. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many g make one kg. There are 1000 g in 1 kg.1 kg = 1000 g
- Multiply by 1000. Changing to a smaller unit needs more of them, so the number gets bigger: multiply.2.45000000000000017763568394 x 1000 = 2450.00000000000017763568394
- Write the answer with the new unit. Keep the same measure, in the new unit.2450.00000000000017763568394 g
- Write the answer. 2450.00000000000017763568394 g
Check. 2450.00000000000017763568394 g is the same length, mass or volume as 2.45000000000000017763568394 kg. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many cm make one m. There are 100 cm in 1 m.1 m = 100 cm
- Divide by 100. Changing to a bigger unit needs fewer of them, so the number gets smaller: divide.480 / 100 = 4.8
- Write the answer with the new unit. Keep the same measure, in the new unit.4.8 m
- Write the answer. 4.8 m
Check. 4.8 m is the same length, mass or volume as 480 cm. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many m make one km. There are 1000 m in 1 km.1 km = 1000 m
- Multiply by 1000. Changing to a smaller unit needs more of them, so the number gets bigger: multiply.0.05999999999999999777955395075 x 1000 = 59.99999999999999777955395075
- Write the answer with the new unit. Keep the same measure, in the new unit.59.99999999999999777955395075 m
- Write the answer. 59.99999999999999777955395075 m
Check. 59.99999999999999777955395075 m is the same length, mass or volume as 0.05999999999999999777955395075 km. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many mm make one cm. There are 10 mm in 1 cm.1 cm = 10 mm
- Divide by 10. Changing to a bigger unit needs fewer of them, so the number gets smaller: divide.750 / 10 = 75
- Write the answer with the new unit. Keep the same measure, in the new unit.75 cm
- Write the answer. 75 cm
Check. 75 cm is the same length, mass or volume as 750 mm. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many ml make one l. There are 1000 ml in 1 l.1 l = 1000 ml
- Multiply by 1000. Changing to a smaller unit needs more of them, so the number gets bigger: multiply.6.5 x 1000 = 6500
- Write the answer with the new unit. Keep the same measure, in the new unit.6500 ml
- Write the answer. 6500 ml
Check. 6500 ml is the same length, mass or volume as 6.5 l. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many g make one kg. There are 1000 g in 1 kg.1 kg = 1000 g
- Divide by 1000. Changing to a bigger unit needs fewer of them, so the number gets smaller: divide.1250 / 1000 = 1.25
- Write the answer with the new unit. Keep the same measure, in the new unit.1.25 kg
- Write the answer. 1.25 kg
Check. 1.25 kg is the same length, mass or volume as 1250 g. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Change the litres to millilitres, then divide by 250.
- Change to ml. 1.5 litres = 1500 ml.1500 ml
- Divide. 1500 / 250 = 6 glasses.6
- Write the answer. 6
Check. 6 x 250 = 1500. ✓
Method. Change the mass to grams, then divide.
- Change to grams. 2.4 kg = 2400 g.2400 g
- Divide. 2400 / 150 = 16 cakes.16
- Write the answer. 16
Check. 16 x 150 = 2400. ✓
Method. Test each choice against the question.
- Read what the question asks. Decide what the answer must do or show.
- Test the choice. 1 km is 1000 m, so half a kilometre is 500 m.No, 0.5 km is 500 m fits
- Reject the other choices. Half of 1000 is 500, not 50.Yes, 0.5 km is 50 m do not fit
- Write the answer. No, 0.5 km is 500 m
Check. No, 0.5 km is 500 m is the one that fits. ✓
Method. Test each option.
- Check each option. Test each one against the rule or the calculation.
- Tick the true ones. These are the correct metric facts: 100 cm in a metre and 10 mm in a centimetre.1 m = 100 cm, 1 cm = 10 mm
- Leave the others unticked. These do not match.1 kg = 100 g, 1 litre = 100 ml, 1 km = 100 m are not ticked
- Write the answer. 1 m = 100 cm, 1 cm = 10 mm
Check. Each ticked option is true. ✓
Watch out. 1 kg is 1000 g, 1 litre is 1000 ml and 1 km is 1000 m.
Method. Multiply by 100.
- Multiply. 3.25 x 100 = 325.325 cm
- Write the answer. 325 cm
Check. 325 / 100 = 3.25. ✓
Method. 350 ml is 0.35 litres, so add it to the 2 litres.
- Change ml to litres. 350 / 1000 = 0.35 litres.0.35 litres
- Add. 2 + 0.35 = 2.35 litres.2.35 litres
- Write the answer. 2.35 litres
Check. 2.35 x 1000 = 2350 ml. ✓
Method. Change to the same unit first.
- Change metres to centimetres. 4 m = 400 cm.400 cm
- Divide. 400 / 80 = 5 pipes.5
- Write the answer. Five pipes, because 4 m is 400 cm and 400 / 80 = 5.
Check. 5 x 80 = 400. ✓
Method. Change to the same unit, then add.
- Change 0.8 kg. 0.8 kg = 800 g.800 g
- Add. 800 + 650 = 1450 g.1450 g
- Write the answer. 1450 g
Check. 1450 g = 1.45 kg. ✓
Method. Change litres to millilitres.
- Change 2.4 litres. 2.4 x 1000 = 2400 ml.2400 ml
- Compare. They are the same amount.equal
- Write the answer. 2.4 litres is 2400 ml, so they are the same amount.
Check. 2.4 x 1000 = 2400. ✓
Time, durations and timetables
Rule
There are 60 minutes in an hour, 24 hours in a day and 60 seconds in a minute.
To find a duration, work out the time in minutes for each time, then subtract. Change the answer back to hours and minutes.
Key ideas
- 1 hour = 60 minutes; 1 minute = 60 seconds.
- To find a duration, subtract the start time from the end time.
- Do not write 1 h 75 min: that is 2 h 15 min.
Method. Find the difference between the two times in minutes, then change to hours and minutes.
- Change both times to minutes past midnight. 09:15 is 555 minutes and 11:50 is 710 minutes.555 and 710
- Subtract the start from the end. 710 - 555 = 155 minutes.155 minutes
- Change back to hours and minutes. 155 minutes is 2 hour(s) and 35 minutes.2 h 35 min
- Write the answer. 2 h 35 min
Check. 09:15 + 2 h 35 min = 11:50. ✓
Watch out. Do not count 60 minutes as 100 when you change between hours and minutes.
Method. Find the difference between the two times in minutes, then change to hours and minutes.
- Change both times to minutes past midnight. 08:40 is 520 minutes and 12:05 is 725 minutes.520 and 725
- Subtract the start from the end. 725 - 520 = 205 minutes.205 minutes
- Change back to hours and minutes. 205 minutes is 3 hour(s) and 25 minutes.3 h 25 min
- Write the answer. 3 h 25 min
Check. 08:40 + 3 h 25 min = 12:05. ✓
Watch out. Do not count 60 minutes as 100 when you change between hours and minutes.
Method. Find the difference between the two times in minutes, then change to hours and minutes.
- Change both times to minutes past midnight. 13:20 is 800 minutes and 15:05 is 905 minutes.800 and 905
- Subtract the start from the end. 905 - 800 = 105 minutes.105 minutes
- Change back to hours and minutes. 105 minutes is 1 hour(s) and 45 minutes.1 h 45 min
- Write the answer. 1 h 45 min
Check. 13:20 + 1 h 45 min = 15:05. ✓
Watch out. Do not count 60 minutes as 100 when you change between hours and minutes.
Watch out
Watch out. From 10:45 to 11:20 is 35 minutes, not 75 minutes. Count the minutes after the hour.
Exam tip
Practice guide. Count on from the start time to the next hour, then to the end time.
Exercise 4B Practice: time and durations
Non-calculatorMethod. Find the difference between the two times in minutes, then change to hours and minutes.
- Change both times to minutes past midnight. 07:35 is 455 minutes and 10:10 is 610 minutes.455 and 610
- Subtract the start from the end. 610 - 455 = 155 minutes.155 minutes
- Change back to hours and minutes. 155 minutes is 2 hour(s) and 35 minutes.2 h 35 min
- Write the answer. 2 h 35 min
Check. 07:35 + 2 h 35 min = 10:10. ✓
Watch out. Do not count 60 minutes as 100 when you change between hours and minutes.
Method. Find the difference between the two times in minutes, then change to hours and minutes.
- Change both times to minutes past midnight. 14:25 is 865 minutes and 16:00 is 960 minutes.865 and 960
- Subtract the start from the end. 960 - 865 = 95 minutes.95 minutes
- Change back to hours and minutes. 95 minutes is 1 hour(s) and 35 minutes.1 h 35 min
- Write the answer. 1 h 35 min
Check. 14:25 + 1 h 35 min = 16:00. ✓
Watch out. Do not count 60 minutes as 100 when you change between hours and minutes.
Method. Find the difference between the two times in minutes, then change to hours and minutes.
- Change both times to minutes past midnight. 06:50 is 410 minutes and 09:05 is 545 minutes.410 and 545
- Subtract the start from the end. 545 - 410 = 135 minutes.135 minutes
- Change back to hours and minutes. 135 minutes is 2 hour(s) and 15 minutes.2 h 15 min
- Write the answer. 2 h 15 min
Check. 06:50 + 2 h 15 min = 09:05. ✓
Watch out. Do not count 60 minutes as 100 when you change between hours and minutes.
Method. Find the difference between the two times in minutes, then change to hours and minutes.
- Change both times to minutes past midnight. 10:45 is 645 minutes and 11:20 is 680 minutes.645 and 680
- Subtract the start from the end. 680 - 645 = 35 minutes.35 minutes
- Change back to hours and minutes. 35 minutes is 0 hour(s) and 35 minutes.35 min
- Write the answer. 35 min
Check. 10:45 + 35 min = 11:20. ✓
Watch out. Do not count 60 minutes as 100 when you change between hours and minutes.
Method. Add the journey time to the start time.
- Add 35 minutes to reach 09:00. 08:25 + 35 min = 09:00.09:00
- Add the other 12 minutes. 47 - 35 = 12, so 09:00 + 12 min = 09:12.09:12
- Write the answer. 09:12
Check. 09:12 - 08:25 = 47 minutes. ✓
Method. Add the hours, then the minutes.
- Add 2 hours. 19:40 + 2 h = 21:40.21:40
- Add 15 minutes. 21:40 + 15 min = 21:55.21:55
- Write the answer. 21:55
Check. 21:55 - 19:40 = 2 h 15 min. ✓
Method. Change the hours to minutes, then add the minutes.
- Hours to minutes. 3 x 60 = 180 minutes.180
- Add. 180 + 20 = 200 minutes.200
- Write the answer. 200
Check. 200 / 60 = 3 h 20 min. ✓
Method. One minute has 60 seconds.
- Multiply. 4 x 60 = 240 seconds.240
- Write the answer. 240
Check. 240 / 60 = 4. ✓
Method. Add the lateness to the due time.
- Add 10 minutes. 13:50 + 10 min = 14:00.14:00
- Add the rest. 35 - 10 = 25, so 14:00 + 25 min = 14:25.14:25
- Write the answer. 14:25
Check. 14:25 - 13:50 = 35 min. ✓
Method. Change the hour to minutes first.
- Change the hour. 1 hour is 60 minutes.60
- Add the minutes. 60 + 30 = 90 minutes.90
- Write the answer. No, because 1 hour is 60 minutes, so 1 hour 30 minutes is 90 minutes.
Check. 60 + 30 = 90. ✓
Method. Find the difference in minutes.
- Count to 17:00. 16:10 to 17:00 is 50 minutes.50
- Add the last 5 minutes. 50 + 5 = 55 minutes.55
- Write the answer. 55
Check. 16:10 + 55 min = 17:05. ✓
Method. Test each choice against the question.
- Read what the question asks. Decide what the answer must do or show.
- Test the choice. 08:15 minus 07:50 is 25 minutes: 10 minutes to 08:00 and 15 more.25 minutes fits
- Reject the other choices. 35 and 65 do not come from counting from 07:50 to 08:15.35 minutes and 65 minutes do not fit
- Write the answer. 25 minutes
Check. 25 minutes is the one that fits. ✓
Method. Work out the total time, then take away the break.
- Total time. 08:50 to 15:20 is 6 hours 30 minutes = 390 minutes.390 minutes
- Take away the break. 390 - 80 = 310 minutes.310
- Write the answer. 310
Check. 310 + 80 = 390. ✓
Method. Add 2 hours, then 45 minutes.
- Add 2 hours. 11:30 + 2 h = 13:30.13:30
- Add 45 minutes. 13:30 + 45 min = 14:15.14:15
- Write the answer. 14:15
Check. 14:15 - 11:30 = 2 h 45 min. ✓
Miles, kilometres and approximate imperial units
Rule
Approximate conversions: 1 mile is about 1.6 km. 1 kg is about 2.2 pounds (lb). 1 inch is about 2.5 cm. 1 litre is about 1.75 pints.
These are estimates, so the answer is about a number. Multiply by the rule, then round.
Key ideas
- 5 miles is about 8 km, so 10 miles is about 16 km.
- An approximate conversion gives an answer with about in front.
- Round to a sensible number of whole units.
Method. Multiply by the approximate conversion factor, then round.
- Use the approximate rule: 1 mile is about 1.6 km. The rule is only an estimate, so the answer is about this amount.5 miles x 1.6 = 8.00
- Round to the nearest whole number. Round to the nearest whole number for a sensible answer.about 8 km
- Write the answer. about 8 km
Check. 5 x 1.6 is about 8. ✓
Watch out. Imperial and metric conversions are approximate. Write about in your answer.
Method. Multiply by the approximate conversion factor, then round.
- Use the approximate rule: 1 kg is about 2.2 pounds. The rule is only an estimate, so the answer is about this amount.60 kg x 2.2 = 132.00
- Round to the nearest whole number. Round to the nearest whole number for a sensible answer.about 132 pounds
- Write the answer. about 132 pounds
Check. 60 x 2.2 is about 132. ✓
Watch out. Imperial and metric conversions are approximate. Write about in your answer.
Method. Multiply by the approximate conversion factor, then round.
- Use the approximate rule: 1 inch is about 2.5 cm. The rule is only an estimate, so the answer is about this amount.20 inches x 2.5 = 50.00
- Round to the nearest whole number. Round to the nearest whole number for a sensible answer.about 50 cm
- Write the answer. about 50 cm
Check. 20 x 2.5 is about 50. ✓
Watch out. Imperial and metric conversions are approximate. Write about in your answer.
Watch out
Watch out. A mile is longer than a kilometre. 10 miles is about 16 km, not 10 km.
Exam tip
Practice guide. Use 5 miles = 8 km as a check when you are not sure of the rule.
Exercise 4C Practice: miles, kilometres and imperial units
Non-calculatorMethod. Multiply by the approximate conversion factor, then round.
- Use the approximate rule: 1 mile is about 1.6 km. The rule is only an estimate, so the answer is about this amount.10 miles x 1.6 = 16.00
- Round to the nearest whole number. Round to the nearest whole number for a sensible answer.about 16 km
- Write the answer. about 16 km
Check. 10 x 1.6 is about 16. ✓
Watch out. Imperial and metric conversions are approximate. Write about in your answer.
Method. Multiply by the approximate conversion factor, then round.
- Use the approximate rule: 1 mile is about 1.6 km. The rule is only an estimate, so the answer is about this amount.26 miles x 1.6 = 41.60
- Round to the nearest whole number. Round to the nearest whole number for a sensible answer.about 42 km
- Write the answer. about 42 km
Check. 26 x 1.6 is about 42. ✓
Watch out. Imperial and metric conversions are approximate. Write about in your answer.
Method. Multiply by the approximate conversion factor, then round.
- Use the approximate rule: 1 kg is about 2.2 pounds. The rule is only an estimate, so the answer is about this amount.4 kg x 2.2 = 8.80
- Round to the nearest whole number. Round to the nearest whole number for a sensible answer.about 9 pounds
- Write the answer. about 9 pounds
Check. 4 x 2.2 is about 9. ✓
Watch out. Imperial and metric conversions are approximate. Write about in your answer.
Method. Multiply by the approximate conversion factor, then round.
- Use the approximate rule: 1 litre is about 1.75 pints. The rule is only an estimate, so the answer is about this amount.3 litres x 1.75 = 5.25
- Round to the nearest whole number. Round to the nearest whole number for a sensible answer.about 5 pints
- Write the answer. about 5 pints
Check. 3 x 1.75 is about 5. ✓
Watch out. Imperial and metric conversions are approximate. Write about in your answer.
Method. Multiply by the approximate conversion factor, then round.
- Use the approximate rule: 1 inch is about 2.5 cm. The rule is only an estimate, so the answer is about this amount.2 inches x 2.5 = 5.00
- Round to the nearest whole number. Round to the nearest whole number for a sensible answer.about 5 cm
- Write the answer. about 5 cm
Check. 2 x 2.5 is about 5. ✓
Watch out. Imperial and metric conversions are approximate. Write about in your answer.
Method. Test each choice against the question.
- Read what the question asks. Decide what the answer must do or show.
- Test the choice. 10 km is about 10 / 1.6 = 6 miles, because a mile is longer than a kilometre.about 6 miles fits
- Reject the other choices. About 16 miles would be 10 miles in km, the wrong way round. About 10 miles is the same number, which is wrong.about 16 miles and about 10 miles do not fit
- Write the answer. about 6 miles
Check. about 6 miles is the one that fits. ✓
Method. Multiply the miles by 1.6.
- Multiply. 20 x 1.6 = 32.32 km
- Write the answer. 32 km
Check. 32 / 1.6 = 20. ✓
Method. Convert one of the distances to the other unit.
- Convert 10 miles. 10 x 1.6 = 16 km.16 km
- Compare. 16 km is more than 10 km.10 miles is longer
- Write the answer. Because 10 miles is about 16 km, which is longer than 10 km.
Check. 16 > 10. ✓
Method. Multiply by 2.2, then round to the nearest whole number.
- Multiply. 3.5 x 2.2 = 7.7.7.7
- Round. 7.7 rounds to 8.8 pounds
- Write the answer. 8 pounds
Check. 8 / 2.2 is about 3.6, close to 3.5. ✓
Method. Find the total miles, then convert.
- Total miles. 15 + 8 = 23 miles.23
- Convert. 23 x 1.6 = 36.8, which rounds to 37 km.37 km
- Write the answer. 37 km
Check. 23 x 1.6 = 36.8. ✓
Method. Test each option.
- Check each option. Test each one against the rule or the calculation.
- Tick the true ones. 5 miles is about 8 km, and 2 inches is about 5 cm (1 inch is about 2.5 cm).5 miles is about 8 km, 2 inches is about 5 cm
- Leave the others unticked. These do not match.1 kg is about 10 pounds, 1 litre is about 5 pints are not ticked
- Write the answer. 5 miles is about 8 km, 2 inches is about 5 cm
Check. Each ticked option is true. ✓
Watch out. 1 kg is about 2.2 pounds, not 10. 1 litre is about 1.75 pints, not 5.
Method. Use 8 km = 5 miles to scale.
- Find 1 km. 80 / 8 = 10, so 80 km = 10 lots of 8 km.10
- Multiply. 10 x 5 = 50 miles.50 miles
- Write the answer. 50 miles
Check. 8 km = 5 miles, so 80 km = 50 miles. ✓
Perimeter and area of rectangles, triangles, parallelograms and composite shapes
Rule
Rectangle: area = length x width. Triangle: area = base x perpendicular height / 2. Parallelogram: area = base x perpendicular height.
For a shape made of rectangles, find each area and add them. For perimeter, add all the outside sides.
Key ideas
- Use the perpendicular height for triangles and parallelograms.
- A triangle is half of a rectangle with the same base and height.
- The perimeter of a rectilinear shape is the total length of its outside edges.
Method. Multiply the length by the width.
- Write the formula. Area of a rectangle = length x width.12 x 7
- Multiply. Multiply the length by the width.12 x 7 = 84
- Write the units as square units. The area is measured in square cm.84 cm²
- Write the answer. 84 cm²
Check. 84 / 12 = 7. ✓
Watch out. Area is measured in square units, so the answer ends with a small 2, such as cm².
Method. Multiply the base by the height, then halve.
- Write the formula. Area of a triangle = base x height / 2.10 x 6 / 2
- Multiply the base and the height. Multiply first.10 x 6 = 60
- Halve the answer. A triangle is half of a rectangle with the same base and height.60 / 2 = 30
- Write the answer. Square units for area.30 cm²
- Write the answer. 30 cm²
Check. A rectangle 10 by 6 has area 60, and half of it is 30. ✓
Watch out. Use the perpendicular height, not the slanted side.
Method. Split the shape into rectangles, find each area, then add.
- Split the shape into two rectangles. Rectangle 1 is 6 cm by 4 cm; rectangle 2 is 3 cm by 2 cm.6 x 4 and 3 x 2
- Find each area. Multiply the length and width of each rectangle.24 and 6
- Add the areas. The total area is the sum of the two parts.24 + 6 = 30
- Write the answer. Square units for area.30 cm²
- Write the answer. 30 cm²
Check. 24 + 6 = 30. ✓
Watch out. Check that the two rectangles do not overlap.
Watch out
Watch out. Do not use the slanted side of a triangle or a parallelogram. Use the perpendicular height.
Exam tip
Practice guide. Draw the shape and label the lengths before you multiply.
Exercise 4D Practice: perimeter and area
Non-calculatorMethod. Multiply the length by the width.
- Write the formula. Area of a rectangle = length x width.15 x 8
- Multiply. Multiply the length by the width.15 x 8 = 120
- Write the units as square units. The area is measured in square m.120 m²
- Write the answer. 120 m²
Check. 120 / 15 = 8. ✓
Watch out. Area is measured in square units, so the answer ends with a small 2, such as cm².
Method. Multiply the base by the height, then halve.
- Write the formula. Area of a triangle = base x height / 2.7 x 4 / 2
- Multiply the base and the height. Multiply first.7 x 4 = 28
- Halve the answer. A triangle is half of a rectangle with the same base and height.28 / 2 = 14
- Write the answer. Square units for area.14 cm²
- Write the answer. 14 cm²
Check. A rectangle 7 by 4 has area 28, and half of it is 14. ✓
Watch out. Use the perpendicular height, not the slanted side.
Method. Multiply the base by the height, then halve.
- Write the formula. Area of a triangle = base x height / 2.9 x 6 / 2
- Multiply the base and the height. Multiply first.9 x 6 = 54
- Halve the answer. A triangle is half of a rectangle with the same base and height.54 / 2 = 27
- Write the answer. Square units for area.27 cm²
- Write the answer. 27 cm²
Check. A rectangle 9 by 6 has area 54, and half of it is 27. ✓
Watch out. Use the perpendicular height, not the slanted side.
Method. Multiply the base by the perpendicular height. No halving is needed.
- Write the formula. Area of a parallelogram = base x perpendicular height.11 x 5
- Multiply. Multiply the base by the perpendicular height.11 x 5 = 55
- Write the answer. Square units for area.55 cm²
- Write the answer. 55 cm²
Check. A rectangle 11 by 5 has the same area. ✓
Watch out. A parallelogram is not halved, unlike a triangle with the same base and height.
Method. Split the shape into rectangles, find each area, then add.
- Split the shape into two rectangles. Rectangle 1 is 8 m by 5 m; rectangle 2 is 4 m by 3 m.8 x 5 and 4 x 3
- Find each area. Multiply the length and width of each rectangle.40 and 12
- Add the areas. The total area is the sum of the two parts.40 + 12 = 52
- Write the answer. Square units for area.52 m²
- Write the answer. 52 m²
Check. 40 + 12 = 52. ✓
Watch out. Check that the two rectangles do not overlap.
Method. Split the shape into rectangles, find each area, then add.
- Split the shape into two rectangles. Rectangle 1 is 10 cm by 3 cm; rectangle 2 is 4 cm by 6 cm.10 x 3 and 4 x 6
- Find each area. Multiply the length and width of each rectangle.30 and 24
- Add the areas. The total area is the sum of the two parts.30 + 24 = 54
- Write the answer. Square units for area.54 cm²
- Write the answer. 54 cm²
Check. 30 + 24 = 54. ✓
Watch out. Check that the two rectangles do not overlap.
Method. Add all four sides, or use 2 x (length + width).
- Add the four sides. 9 + 4 + 9 + 4 = 26.26
- Check. 2 x (9 + 4) = 2 x 13 = 26.26
- Write the answer. 26
Check. 26 / 2 = 13 = 9 + 4. ✓
Method. A cut-out corner does not change the outside perimeter, so use the big rectangle.
- Outside sides. The notch moves inwards, but the outside edges still add to the whole rectangle.10 + 6 + 10 + 6
- Add. 10 + 6 + 10 + 6 = 32 m.32 m
- Write the answer. 32
Check. 2 x (10 + 6) = 32. ✓
Watch out. A notch cut from a corner does not change the perimeter, so the big rectangle gives the answer.
Method. Find the area of the whole poster with the border, then take away the poster.
- Outside size. With 5 cm on each side the length is 40 + 10 = 50 cm, and the width is 30 + 10 = 40 cm.50 x 40
- Area with border. 50 x 40 = 2000 square cm.2000
- Area of the border. 2000 - (40 x 30) = 2000 - 1200 = 800 square cm.800
- Write the answer. 800
Check. 1200 + 800 = 2000. ✓
Method. Use base x height / 2.
- Multiply. 8 x 5 = 40.40
- Halve. 40 / 2 = 20 square cm.20 square cm
- Write the answer. 20 square cm
Check. Sam forgot to halve. ✓
Method. Test each choice against the question.
- Read what the question asks. Decide what the answer must do or show.
- Test the choice. A parallelogram is the same as a rectangle with the same base and height, so its area is base x height. A triangle is half of that.the parallelogram fits
- Reject the other choices. The triangle has half the area, so the others are wrong.the triangle and they are the same do not fit
- Write the answer. the parallelogram
Check. the parallelogram is the one that fits. ✓
Method. Use area = base x height / 2, and work backwards.
- Double the area. 30 x 2 = 60.60
- Divide by the base. 60 / 10 = 6 cm.6 cm
- Write the answer. 6
Check. 10 x 6 / 2 = 30. ✓
Method. Compare the perpendicular height with the slanted side.
- Identify the height. The perpendicular height goes straight across, at right angles to the base.perpendicular
- Compare. The slanted side is longer than the height, so 5 cm is a sensible height.5 cm < 9 cm
- Write the answer. Because the perpendicular height is the straight-up distance, which can be shorter than the slanted side.
Check. The perpendicular is shorter than the slanted side. ✓
Method. Split the shape into rectangles, find each area, then add.
- Split the shape into two rectangles. Rectangle 1 is 12 cm by 2 cm; rectangle 2 is 5 cm by 3 cm.12 x 2 and 5 x 3
- Find each area. Multiply the length and width of each rectangle.24 and 15
- Add the areas. The total area is the sum of the two parts.24 + 15 = 39
- Write the answer. Square units for area.39 cm²
- Write the answer. 39 cm²
Check. 24 + 15 = 39. ✓
Watch out. Check that the two rectangles do not overlap.
Method. Find the area of the rectangle, then take away the triangle.
- Rectangle. 14 x 6 = 84 square cm.84
- Triangle. 6 x 4 / 2 = 12 square cm.12
- Left. 84 - 12 = 72 square cm.72
- Write the answer. 72
Check. 72 + 12 = 84. ✓
Same area, different perimeters, and volume of cuboids
Rule
Rectangles with the same area can have different perimeters. The closer the length and width, the smaller the perimeter.
Volume of a cuboid = length x width x height. Cubic units are written as cm3.
Key ideas
- Same area, different perimeter: a square has the smallest perimeter for a given area.
- Perimeter = 2 x (length + width).
- Volume is the number of unit cubes that fill the box.
Method. List the pairs that multiply to the area, then find each perimeter.
- List the whole-number pairs that multiply to the area. Each pair of sides gives area 24.1 x 24; 2 x 12; 3 x 8; 4 x 6
- Work out each perimeter. Perimeter = 2 x (length + width).1 by 24 gives 50; 2 by 12 gives 28; 3 by 8 gives 22; 4 by 6 gives 20
- Choose the smallest perimeter. The smallest perimeter is the one with the sides closest in length.4 by 6 (perimeter 20)
- Write the answer. 4 by 6 (perimeter 20)
Check. The closest pair of sides gives the smallest perimeter. ✓
Watch out. The same area can have very different perimeters: a long thin rectangle has a bigger perimeter than a square.
Method. Multiply the length, width and height.
- Write the formula. Volume of a cuboid = length x width x height.4 x 3 x 5
- Multiply. Multiply the three lengths.4 x 3 = 12, then 12 x 5 = 60
- Write the units. Cubic units for volume.60 cm³
- Write the answer. 60 cm³
Check. 4 x 3 x 5 = 60. ✓
Watch out. Volume is measured in cubic units, so the answer ends with a small 3, such as cm³.
Method. Work out the volume of each shape.
- Cube. Volume = 4 x 4 x 4 = 64 cm3.64 cm³
- Cuboid. Volume = 6 x 4 x 3 = 72 cm3.72 cm³
- Compare. 72 is more than 64, so the cuboid has the bigger volume.cuboid
- Write the answer. cuboid
Check. 72 > 64. ✓
Watch out
Watch out. A long thin rectangle can have a much bigger perimeter than a square with the same area.
Exam tip
Practice guide. List the pairs of sides that multiply to the area, then work out each perimeter.
Exercise 4E Practice: same area and volume
Non-calculatorMethod. List the pairs that multiply to the area, then find each perimeter.
- List the whole-number pairs that multiply to the area. Each pair of sides gives area 36.1 x 36; 2 x 18; 3 x 12; 4 x 9; 6 x 6
- Work out each perimeter. Perimeter = 2 x (length + width).1 by 36 gives 74; 2 by 18 gives 40; 3 by 12 gives 30; 4 by 9 gives 26; 6 by 6 gives 24
- Choose the smallest perimeter. The smallest perimeter is the one with the sides closest in length.6 by 6 (perimeter 24)
- Write the answer. 6 by 6 (perimeter 24)
Check. The closest pair of sides gives the smallest perimeter. ✓
Watch out. The same area can have very different perimeters: a long thin rectangle has a bigger perimeter than a square.
Method. List the pairs that multiply to the area, then find each perimeter.
- List the whole-number pairs that multiply to the area. Each pair of sides gives area 20.1 x 20; 2 x 10; 4 x 5
- Work out each perimeter. Perimeter = 2 x (length + width).1 by 20 gives 42; 2 by 10 gives 24; 4 by 5 gives 18
- Choose the smallest perimeter. The smallest perimeter is the one with the sides closest in length.4 by 5 (perimeter 18)
- Write the answer. 4 by 5 (perimeter 18)
Check. The closest pair of sides gives the smallest perimeter. ✓
Watch out. The same area can have very different perimeters: a long thin rectangle has a bigger perimeter than a square.
Method. Multiply the length, width and height.
- Write the formula. Volume of a cuboid = length x width x height.6 x 2 x 5
- Multiply. Multiply the three lengths.6 x 2 = 12, then 12 x 5 = 60
- Write the units. Cubic units for volume.60 cm³
- Write the answer. 60 cm³
Check. 6 x 2 x 5 = 60. ✓
Watch out. Volume is measured in cubic units, so the answer ends with a small 3, such as cm³.
Method. Multiply the length, width and height.
- Write the formula. Volume of a cuboid = length x width x height.3 x 3 x 3
- Multiply. Multiply the three lengths.3 x 3 = 9, then 9 x 3 = 27
- Write the units. Cubic units for volume.27 cm³
- Write the answer. 27 cm³
Check. 3 x 3 x 3 = 27. ✓
Watch out. Volume is measured in cubic units, so the answer ends with a small 3, such as cm³.
Method. Multiply the length, width and height.
- Write the formula. Volume of a cuboid = length x width x height.10 x 4 x 2
- Multiply. Multiply the three lengths.10 x 4 = 40, then 40 x 2 = 80
- Write the units. Cubic units for volume.80 cm³
- Write the answer. 80 cm³
Check. 10 x 4 x 2 = 80. ✓
Watch out. Volume is measured in cubic units, so the answer ends with a small 3, such as cm³.
Method. Work out both volumes.
- Cube. 5 x 5 x 5 = 125 cm3.125
- Cuboid. 4 x 6 x 4 = 96 cm3.96
- Compare. 125 is more than 96, so the cube holds more.5 cm cube
- Write the answer. 5 cm cube
Check. 125 > 96. ✓
Method. Divide the volume by the length and the width.
- Area of the base. 6 x 4 = 24 cm2.24
- Height. 48 / 24 = 2 cm.2
- Write the answer. 2
Check. 24 x 2 = 48. ✓
Method. Test each choice against the question.
- Read what the question asks. Decide what the answer must do or show.
- Test the choice. 3 + 4 = 7, and the perimeter is 14 cm, which is the smallest of the three.3 cm by 4 cm fits
- Reject the other choices. 2 by 6 has a perimeter of 16 and 1 by 12 has a perimeter of 26.2 cm by 6 cm and 1 cm by 12 cm do not fit
- Write the answer. 3 cm by 4 cm
Check. 3 cm by 4 cm is the one that fits. ✓
Method. Work out both perimeters.
- Perimeter of 6 by 2. 2 x (6 + 2) = 16 cm.16 cm
- Perimeter of 4 by 3. 2 x (4 + 3) = 14 cm.14 cm
- Write the answer. Because the perimeter depends on the total length of the sides, and 6 + 2 = 8 is not the same as 4 + 3 = 7.
Check. 16 and 14 are different. ✓
Method. The number of cubes is the same as the volume.
- Volume. 10 x 5 x 2 = 100 cm3.100
- Count. Each 1 cm cube is 1 cm3, so 100 cubes fill it.100
- Write the answer. 100
Check. 100 / (5 x 2) = 10. ✓
Method. List the pairs that multiply to the area, then find each perimeter.
- List the whole-number pairs that multiply to the area. Each pair of sides gives area 16.1 x 16; 2 x 8; 4 x 4
- Work out each perimeter. Perimeter = 2 x (length + width).1 by 16 gives 34; 2 by 8 gives 20; 4 by 4 gives 16
- Choose the smallest perimeter. The smallest perimeter is the one with the sides closest in length.4 by 4 (perimeter 16)
- Write the answer. 4 by 4 (perimeter 16)
Check. The closest pair of sides gives the smallest perimeter. ✓
Watch out. The same area can have very different perimeters: a long thin rectangle has a bigger perimeter than a square.
Method. Find the width from the area, then the perimeter.
- Width. 30 / 6 = 5 cm.5 cm
- Perimeter. 2 x (6 + 5) = 22 cm.22 cm
- Write the answer. 5 cm and 22 cm
Check. 6 x 5 = 30 and 2 x 11 = 22. ✓
Method. Work out both perimeters.
- 25 by 1. 2 x (25 + 1) = 52 m.52 m
- 5 by 5. 2 x (5 + 5) = 20 m.20 m
- Write the answer. 5 m by 5 m, because its perimeter is 20 m, which is less than the 52 m of 25 by 1.
Check. 20 is less than 52. ✓
Chapter summary
| Skill | Method |
|---|---|
| Metric conversions | Smaller unit: multiply. Bigger unit: divide. 1 km = 1000 m; 1 kg = 1000 g; 1 l = 1000 ml. |
| Time | Change to minutes, subtract, then change back. 1 hour = 60 minutes. |
| Miles and kilometres | About 1.6 km to 1 mile; 5 miles is about 8 km. |
| Area of a rectangle | Length x width. |
| Area of a triangle | Base x perpendicular height / 2. |
| Area of a parallelogram | Base x perpendicular height. |
| Perimeter | The total length of the outside edges. |
| Volume of a cuboid | Length x width x height, in cubic units. |
Can you…?
- I can convert between metric units, including decimals
- I can work out a duration and read a timetable
- I can use an approximate conversion between miles and kilometres
- I can find the area of a rectangle, triangle, parallelogram and composite shape
- I can explain why shapes with the same area can have different perimeters
- I can find the volume of a cuboid and compare two volumes
Key terms
- perpendicular height
- the straight height at right angles to the base
- perimeter
- the total distance around the outside of a shape
- composite shape
- a shape made from two or more simpler shapes
- volume
- the amount of space inside a 3-D shape, measured in cubic units
- approximately
- close to, but not exactly equal to
- duration
- the length of time between a start and an end
Exercise 4Z Check-up
Non-calculatorMethod. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many g make one kg. There are 1000 g in 1 kg.1 kg = 1000 g
- Multiply by 1000. Changing to a smaller unit needs more of them, so the number gets bigger: multiply.4.25 x 1000 = 4250
- Write the answer with the new unit. Keep the same measure, in the new unit.4250 g
- Write the answer. 4250 g
Check. 4250 g is the same length, mass or volume as 4.25 kg. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many ml make one l. There are 1000 ml in 1 l.1 l = 1000 ml
- Divide by 1000. Changing to a bigger unit needs fewer of them, so the number gets smaller: divide.3600 / 1000 = 3.6
- Write the answer with the new unit. Keep the same measure, in the new unit.3.6 l
- Write the answer. 3.6 l
Check. 3.6 l is the same length, mass or volume as 3600 ml. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the difference between the two times in minutes, then change to hours and minutes.
- Change both times to minutes past midnight. 15:30 is 930 minutes and 17:05 is 1025 minutes.930 and 1025
- Subtract the start from the end. 1025 - 930 = 95 minutes.95 minutes
- Change back to hours and minutes. 95 minutes is 1 hour(s) and 35 minutes.1 h 35 min
- Write the answer. 1 h 35 min
Check. 15:30 + 1 h 35 min = 17:05. ✓
Watch out. Do not count 60 minutes as 100 when you change between hours and minutes.
Method. Multiply by the approximate conversion factor, then round.
- Use the approximate rule: 1 mile is about 1.6 km. The rule is only an estimate, so the answer is about this amount.15 miles x 1.6 = 24.00
- Round to the nearest whole number. Round to the nearest whole number for a sensible answer.about 24 km
- Write the answer. about 24 km
Check. 15 x 1.6 is about 24. ✓
Watch out. Imperial and metric conversions are approximate. Write about in your answer.
Method. Multiply the length by the width.
- Write the formula. Area of a rectangle = length x width.14 x 9
- Multiply. Multiply the length by the width.14 x 9 = 126
- Write the units as square units. The area is measured in square cm.126 cm²
- Write the answer. 126 cm²
Check. 126 / 14 = 9. ✓
Watch out. Area is measured in square units, so the answer ends with a small 2, such as cm².
Method. Multiply the base by the height, then halve.
- Write the formula. Area of a triangle = base x height / 2.12 x 5 / 2
- Multiply the base and the height. Multiply first.12 x 5 = 60
- Halve the answer. A triangle is half of a rectangle with the same base and height.60 / 2 = 30
- Write the answer. Square units for area.30 m²
- Write the answer. 30 m²
Check. A rectangle 12 by 5 has area 60, and half of it is 30. ✓
Watch out. Use the perpendicular height, not the slanted side.
Method. Multiply the base by the perpendicular height. No halving is needed.
- Write the formula. Area of a parallelogram = base x perpendicular height.8 x 7
- Multiply. Multiply the base by the perpendicular height.8 x 7 = 56
- Write the answer. Square units for area.56 cm²
- Write the answer. 56 cm²
Check. A rectangle 8 by 7 has the same area. ✓
Watch out. A parallelogram is not halved, unlike a triangle with the same base and height.
Method. Split the shape into rectangles, find each area, then add.
- Split the shape into two rectangles. Rectangle 1 is 7 cm by 3 cm; rectangle 2 is 5 cm by 2 cm.7 x 3 and 5 x 2
- Find each area. Multiply the length and width of each rectangle.21 and 10
- Add the areas. The total area is the sum of the two parts.21 + 10 = 31
- Write the answer. Square units for area.31 cm²
- Write the answer. 31 cm²
Check. 21 + 10 = 31. ✓
Watch out. Check that the two rectangles do not overlap.
Method. Multiply the length, width and height.
- Write the formula. Volume of a cuboid = length x width x height.5 x 4 x 3
- Multiply. Multiply the three lengths.5 x 4 = 20, then 20 x 3 = 60
- Write the units. Cubic units for volume.60 cm³
- Write the answer. 60 cm³
Check. 5 x 4 x 3 = 60. ✓
Watch out. Volume is measured in cubic units, so the answer ends with a small 3, such as cm³.
Method. List the pairs that multiply to the area, then find each perimeter.
- List the whole-number pairs that multiply to the area. Each pair of sides gives area 18.1 x 18; 2 x 9; 3 x 6
- Work out each perimeter. Perimeter = 2 x (length + width).1 by 18 gives 38; 2 by 9 gives 22; 3 by 6 gives 18
- Choose the smallest perimeter. The smallest perimeter is the one with the sides closest in length.3 by 6 (perimeter 18)
- Write the answer. 3 by 6 (perimeter 18)
Check. The closest pair of sides gives the smallest perimeter. ✓
Watch out. The same area can have very different perimeters: a long thin rectangle has a bigger perimeter than a square.
Total 24 marks. Allow about 24 minutes.
Exercise 4X Practice test questions
Non-calculatorMethod. Find the number of smaller units in one bigger unit, then multiply or divide.
- Find how many ml make one l. There are 1000 ml in 1 l.1 l = 1000 ml
- Multiply by 1000. Changing to a smaller unit needs more of them, so the number gets bigger: multiply.0.3499999999999999777955395075 x 1000 = 349.9999999999999777955395075
- Write the answer with the new unit. Keep the same measure, in the new unit.349.9999999999999777955395075 ml
- Write the answer. 349.9999999999999777955395075 ml
Check. 349.9999999999999777955395075 ml is the same length, mass or volume as 0.3499999999999999777955395075 l. ✓
Watch out. Going from a bigger unit to a smaller one makes the number bigger.
Method. Find the difference between the two times in minutes, then change to hours and minutes.
- Change both times to minutes past midnight. 11:40 is 700 minutes and 13:15 is 795 minutes.700 and 795
- Subtract the start from the end. 795 - 700 = 95 minutes.95 minutes
- Change back to hours and minutes. 95 minutes is 1 hour(s) and 35 minutes.1 h 35 min
- Write the answer. 1 h 35 min
Check. 11:40 + 1 h 35 min = 13:15. ✓
Watch out. Do not count 60 minutes as 100 when you change between hours and minutes.
Method. Multiply by the approximate conversion factor, then round.
- Use the approximate rule: 1 kg is about 2.2 pounds. The rule is only an estimate, so the answer is about this amount.12 kg x 2.2 = 26.40
- Round to the nearest whole number. Round to the nearest whole number for a sensible answer.about 26 pounds
- Write the answer. about 26 pounds
Check. 12 x 2.2 is about 26. ✓
Watch out. Imperial and metric conversions are approximate. Write about in your answer.
Method. Multiply the base by the height, then halve.
- Write the formula. Area of a triangle = base x height / 2.14 x 9 / 2
- Multiply the base and the height. Multiply first.14 x 9 = 126
- Halve the answer. A triangle is half of a rectangle with the same base and height.126 / 2 = 63
- Write the answer. Square units for area.63 cm²
- Write the answer. 63 cm²
Check. A rectangle 14 by 9 has area 126, and half of it is 63. ✓
Watch out. Use the perpendicular height, not the slanted side.
Method. Split the shape into rectangles, find each area, then add.
- Split the shape into two rectangles. Rectangle 1 is 9 m by 4 m; rectangle 2 is 6 m by 2 m.9 x 4 and 6 x 2
- Find each area. Multiply the length and width of each rectangle.36 and 12
- Add the areas. The total area is the sum of the two parts.36 + 12 = 48
- Write the answer. Square units for area.48 m²
- Write the answer. 48 m²
Check. 36 + 12 = 48. ✓
Watch out. Check that the two rectangles do not overlap.
Method. Multiply the length, width and height.
- Write the formula. Volume of a cuboid = length x width x height.8 x 3 x 2
- Multiply. Multiply the three lengths.8 x 3 = 24, then 24 x 2 = 48
- Write the units. Cubic units for volume.48 cm³
- Write the answer. 48 cm³
Check. 8 x 3 x 2 = 48. ✓
Watch out. Volume is measured in cubic units, so the answer ends with a small 3, such as cm³.
Method. Add the journey time, then the break.
- Add the journey. 08:20 + 1 h 50 min = 10:10.10:10
- Add the break. 10:10 + 25 min = 10:35.10:35
- Write the answer. 10:35
Check. 10:35 - 08:20 = 2 h 15 min. ✓
Method. Change one length to the other unit.
- Change metres to centimetres. 2 m = 2 x 100 cm = 200 cm.200 cm
- Compare. The two lengths are the same.equal
- Write the answer. Because 1 metre is 100 cm, so 2 metres is 2 x 100 = 200 cm.
Check. 2 x 100 = 200. ✓
Method. Divide the volume by the area of the base.
- Use the volume formula. Volume = length x width x height, so length = volume / (width x height).length x 3 x 5 = 60
- Find the length. 60 / (3 x 5) = 60 / 15 = 4 cm.4 cm
- Write the answer. 4
Check. 4 x 3 x 5 = 60. ✓
Method. List the pairs that multiply to 16.
- List pairs. 1 x 16, 2 x 8 and 4 x 4 all make 16.16 square cm
- Perimeters. 1 by 16 is 34 cm; 4 by 4 is 16 cm.34 cm and 16 cm
- Write the answer. 1 cm by 16 cm has a perimeter of 34 cm, and 4 cm by 4 cm has a perimeter of 16 cm.
Check. 2 x (1 + 16) = 34. ✓
Method. Multiply by the approximate conversion factor, then round.
- Use the approximate rule: 1 mile is about 1.6 km. The rule is only an estimate, so the answer is about this amount.50 miles x 1.6 = 80.00
- Round to the nearest whole number. Round to the nearest whole number for a sensible answer.about 80 km
- Write the answer. about 80 km
Check. 50 x 1.6 is about 80. ✓
Watch out. Imperial and metric conversions are approximate. Write about in your answer.
Method. Change the height to centimetres, then divide.
- Change to cm. 2 m = 200 cm.200 cm
- Divide. 200 / 25 = 8 strips.8
- Write the answer. 8 strips
Check. 8 x 25 = 200. ✓