Metres and centimetres · Usually met around P2
Estimating lengths
A step is about 50 cm; arms wide about 1 m.
How to do it
Method
A step is about 50 cm; arms wide about 1 m
8 steps × 50 cm ≈ 4 m
Another way
Compare with what you know
A door is about 2 m tall
In full
Your body is a ruler you always have: a finger is about 1 cm wide, a hand about 10 cm wide, a step about 50 cm, and arms stretched wide about 1 m. To estimate, count how many times you use one: 8 steps of about 50 cm, two steps make about 1 m, so 8 steps are about 4 m. An estimate must make sense: a pencil is never metres long, and a bus is never a few centimetres. Or compare with something you know: a 30 cm ruler, a door about 2 m tall.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
A hand is about 10 cm wide. A desk is about 4 hands wide. About how wide is the desk in centimetres?
Show the answer and working
Answer: 40 cm
4 lots of 10 cm: about 40 cm.
Example 2
About how long is 📎?
- A. 40 cm
- B. 4 m
- C. 40 m
- D. 4 cm
Choose the right answer
Show the answer and working
Answer: D. 4 cm
Compare with what you know: a ruler is about 30 cm, so 📎 is about 4 cm.
Example 3
Each of Ka-yan's steps is about 50 cm. Ka-yan walks 4 steps from the door to the window. About how many metres is that?
Show the answer and working
Answer: 2 m
Two steps are about 100 cm, 1 m; 4 steps are 2 pairs: about 2 m.
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