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Home / Practice / Maths
Millimetres to kilometres, grams to kilograms, and problems that mix two units.
Question 1 of 12
Niamh has 8 m of ribbon. She cuts 8 pieces, each 44 cm long. How much ribbon is left?
The two measurements are in different units, so one has to change before anything can be subtracted. 8 m is 800 cm. The pieces use 8 × 44 = 352 cm. 800 − 352 = 448 cm left. Subtracting 352 from 8 directly would be comparing centimetres with metres. Give the answer in the unit the question asks for, which is not always the one you worked in.
The answer is A. The two measurements are in different units, so one has to change before anything can be subtracted. 8 m is 800 cm. The pieces use 8 × 44 = 352 cm. 800 − 352 = 448 cm left. Subtracting 352 from 8 directly would be comparing centimetres with metres. Give the answer in the unit the question asks for, which is not always the one you worked in.
How many g are there in 11.5 kg?
There are 1,000 g in 1 kg, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 11.5 × 1,000 = 11,500 g. The half matters: half of 1,000 is 500, which is why the answer does not end in zeros the way 11,000 would. Write the unit next to every number. Most lost marks in measures are answers with the wrong unit.
The answer is D. There are 1,000 g in 1 kg, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 11.5 × 1,000 = 11,500 g. The half matters: half of 1,000 is 500, which is why the answer does not end in zeros the way 11,000 would. Write the unit next to every number. Most lost marks in measures are answers with the wrong unit.
How many ml are there in 5.5 litres?
There are 1,000 ml in 1 litres, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 5.5 × 1,000 = 5,500 ml. The half matters: half of 1,000 is 500, which is why the answer does not end in zeros the way 5,000 would. The conversions worth knowing cold are 10, 100 and 1,000. Every metric question uses one of them.
The answer is D. There are 1,000 ml in 1 litres, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 5.5 × 1,000 = 5,500 ml. The half matters: half of 1,000 is 500, which is why the answer does not end in zeros the way 5,000 would. The conversions worth knowing cold are 10, 100 and 1,000. Every metric question uses one of them.
How many mm are there in 88.5 cm?
There are 10 mm in 1 cm, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 88.5 × 10 = 885 mm. The half matters: half of 10 is 5, which is why the answer does not end in zeros the way 880 would. Ask whether the new unit is bigger or smaller. Smaller unit, bigger number — that alone decides multiply or divide.
The answer is C. There are 10 mm in 1 cm, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 88.5 × 10 = 885 mm. The half matters: half of 10 is 5, which is why the answer does not end in zeros the way 880 would. Ask whether the new unit is bigger or smaller. Smaller unit, bigger number — that alone decides multiply or divide.
How many mm are there in 61 cm?
There are 10 mm in 1 cm, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 61 × 10 = 610 mm. Write the unit next to every number. Most lost marks in measures are answers with the wrong unit.
The answer is C. There are 10 mm in 1 cm, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 61 × 10 = 610 mm. Write the unit next to every number. Most lost marks in measures are answers with the wrong unit.
Aisha has 5 m of ribbon. She cuts 4 pieces, each 59 cm long. How much ribbon is left?
The two measurements are in different units, so one has to change before anything can be subtracted. 5 m is 500 cm. The pieces use 4 × 59 = 236 cm. 500 − 236 = 264 cm left. Subtracting 236 from 5 directly would be comparing centimetres with metres. Give the answer in the unit the question asks for, which is not always the one you worked in.
The answer is A. The two measurements are in different units, so one has to change before anything can be subtracted. 5 m is 500 cm. The pieces use 4 × 59 = 236 cm. 500 − 236 = 264 cm left. Subtracting 236 from 5 directly would be comparing centimetres with metres. Give the answer in the unit the question asks for, which is not always the one you worked in.
Isla has 4 m of ribbon. She cuts 4 pieces, each 52 cm long. How much ribbon is left?
The two measurements are in different units, so one has to change before anything can be subtracted. 4 m is 400 cm. The pieces use 4 × 52 = 208 cm. 400 − 208 = 192 cm left. Subtracting 208 from 4 directly would be comparing centimetres with metres. Convert to a single unit before doing any arithmetic. It is the first move, not an afterthought.
The answer is C. The two measurements are in different units, so one has to change before anything can be subtracted. 4 m is 400 cm. The pieces use 4 × 52 = 208 cm. 400 − 208 = 192 cm left. Subtracting 208 from 4 directly would be comparing centimetres with metres. Convert to a single unit before doing any arithmetic. It is the first move, not an afterthought.
How many ml are there in 4 litres?
There are 1,000 ml in 1 litres, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 4 × 1,000 = 4,000 ml. The conversions worth knowing cold are 10, 100 and 1,000. Every metric question uses one of them.
The answer is D. There are 1,000 ml in 1 litres, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 4 × 1,000 = 4,000 ml. The conversions worth knowing cold are 10, 100 and 1,000. Every metric question uses one of them.
Alfie has 8 m of ribbon. She cuts 5 pieces, each 64 cm long. How much ribbon is left?
The two measurements are in different units, so one has to change before anything can be subtracted. 8 m is 800 cm. The pieces use 5 × 64 = 320 cm. 800 − 320 = 480 cm left. Subtracting 320 from 8 directly would be comparing centimetres with metres. Give the answer in the unit the question asks for, which is not always the one you worked in.
The answer is B. The two measurements are in different units, so one has to change before anything can be subtracted. 8 m is 800 cm. The pieces use 5 × 64 = 320 cm. 800 − 320 = 480 cm left. Subtracting 320 from 8 directly would be comparing centimetres with metres. Give the answer in the unit the question asks for, which is not always the one you worked in.
Oliver has 3 m of ribbon. She cuts 6 pieces, each 24 cm long. How much ribbon is left?
The two measurements are in different units, so one has to change before anything can be subtracted. 3 m is 300 cm. The pieces use 6 × 24 = 144 cm. 300 − 144 = 156 cm left. Subtracting 144 from 3 directly would be comparing centimetres with metres. Convert to a single unit before doing any arithmetic. It is the first move, not an afterthought.
The answer is A. The two measurements are in different units, so one has to change before anything can be subtracted. 3 m is 300 cm. The pieces use 6 × 24 = 144 cm. 300 − 144 = 156 cm left. Subtracting 144 from 3 directly would be comparing centimetres with metres. Convert to a single unit before doing any arithmetic. It is the first move, not an afterthought.
How many mm are there in 79 cm?
There are 10 mm in 1 cm, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 79 × 10 = 790 mm. Write the unit next to every number. Most lost marks in measures are answers with the wrong unit.
The answer is B. There are 10 mm in 1 cm, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 79 × 10 = 790 mm. Write the unit next to every number. Most lost marks in measures are answers with the wrong unit.
How many m are there in 10 km?
There are 1,000 m in 1 km, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 10 × 1,000 = 10,000 m. The conversions worth knowing cold are 10, 100 and 1,000. Every metric question uses one of them.
The answer is D. There are 1,000 m in 1 km, and the new unit is smaller, so the number gets bigger: multiply rather than divide. 10 × 1,000 = 10,000 m. The conversions worth knowing cold are 10, 100 and 1,000. Every metric question uses one of them.
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