Metres and centimetres · Usually met around P2
Bigger unit, smaller number
Bigger unit, smaller number; check the units before the numbers.
How to do it
Method
Bigger unit, smaller number; check the units before the numbers
2 m = 200 cm: a metre is longer, so 2 is a smaller number than 200
Another way
Think how many goes it takes
Paper clips take many goes; pencils take far fewer
In full
When you measure the same thing, the longer the unit, the fewer goes it takes, so the number is smaller; a shorter unit gives a bigger number. A rope 2 m long is 2 in metres and 200 in centimetres: the rope hasn't changed. To compare lengths, always look at the units first and change them to the same unit before comparing the numbers: 3 m is longer than 200 cm even though 3 is smaller than 200.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
A rope is 5 m long. Measuring it in metres and in centimetres, which gives the bigger number?
- A. The numbers are the same
- B. Metres give the bigger number
- C. They can't be compared
- D. Centimetres give the bigger number
Choose the right answer
Show the answer and working
Answer: D. Centimetres give the bigger number
A centimetre is shorter, so it takes many more goes: 5 m is 500 cm, and 500 is bigger than 5.
Example 2
3 m is longer than 320 cm.
True or false?
Show the answer and working
Answer: False
Change to the same unit first: 3 m = 300 cm; compare that with 320 cm. Don't just see that 3 is smaller than 320.
Example 3
A ribbon is 60 cm long. Measured with 2 cm clips it is □ clips long; measured with 10 cm rulers it is □ rulers long.
Fill in each box
Show the answer and working
Answer: 30，6
The clips are short, so 30 of them; the rulers are long, so just 6: the same ribbon, the bigger the unit, the smaller the number.
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