Measuring length
Length tells us how long or how tall something is. We measure short things in centimetres (cm) and long things in metres (m).
Key idea / 要点
1 m = 100 cm. A ruler is 30 cm long. A door is about 2 m tall.
Comparing length
We can say which thing is longer or shorter. A pencil that is 15 cm is longer than one that is 9 cm, because 15 is more than 9. To add or take away lengths, keep the same unit and just work with the numbers.
Worked example / 例题
A ribbon is 8 cm long. Another is 5 cm long. How much longer is the first ribbon?
Take away: 8 − 5 = 3. The first ribbon is 3 cm longer.
Remember / 记住
- Use cm for small things, m for big things.
- 1 m = 100 cm.
- Start measuring from 0 on the ruler, not from the edge.
- Write the unit, like cm or m, in your answer.