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Units of measurement Cambridge IGCSE Mathematics revision

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In plain words

Before any calculation, the units have to agree. Mixing centimetres with metres is the easiest way to lose marks on a question you can do. Metric units go up in tens, hundreds and thousands, so converting is only a matter of moving the decimal point.

Three things to know

  1. Length: 10 mm = 1 cm, 100 cm = 1 m, 1000 m = 1 km. Mass: 1000 g = 1 kg, 1000 kg = 1 tonne. Capacity: 1000 ml = 1 litre, and 1 ml = 1 cm³.
  2. Going to a smaller unit, multiply (there will be more of them). Going to a bigger unit, divide.
  3. Area and volume units convert differently: 1 m² = 100 × 100 = 10 000 cm², and 1 m³ = 100 × 100 × 100 = 1 000 000 cm³.

Worked example

Change 2.5 m² into cm².

  1. 1 m = 100 cm, so 1 m² = 100 × 100 = 10 000 cm².
  2. 2.5 × 10 000.
  3. = 25 000 cm².

Tips and tricks

  • For areas, use the conversion twice; for volumes, three times.
  • Sense-check: a smaller unit should give a bigger number.
5 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Units of measurement: 5 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

  1. How many centimetres are there in 2.5 metres?
    • 25
    • 250 (the answer)
    • 2500
    • 0.025

    Multiply by 100.

  2. How many grams are there in 3.2 kg?
    • 32
    • 320
    • 3200 (the answer)
    • 0.0032

    Multiply by 1000.

  3. How many cm² are there in 1 m²?
    • 100
    • 1000
    • 10 000 (the answer)
    • 1 000 000

    100 × 100.

  4. How many millilitres are there in 0.4 litres?
    • 4
    • 40
    • 400 (the answer)
    • 4000

    Multiply by 1000.

  5. What is 450 mm in metres?
    • 45 m
    • 4.5 m
    • 0.45 m (the answer)
    • 0.045 m

    Divide by 1000.

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