Length
Measurement · Length
CBC Grade 5 Mathematics — Length
Lesson Objectives
By the end of this topic, a learner should be able to:
- Identify the kilometre as a unit for measuring longer distances
- Explain the relationship between kilometres and metres
- Convert between kilometres and metres
- Add, subtract, multiply, and divide lengths given in kilometres and metres
- Appreciate the use of kilometres and metres in everyday situations
Length
Length measures how far or how long. For long distances we use the kilometre.
a) The kilometre
A kilometre is 1 000 metres.
It is used for distances between places. From one town to the next, or how far you walk to school.
The short way to write it is km.
b) Converting
To change kilometres to metres, multiply by 1 000.
To change metres to kilometres, divide by 1 000.
A check: metres are smaller, so there are more of them. Kilometres always give the smaller number.
c) Adding and subtracting
Add the metres first, then the kilometres.
The metres may come to 1 000 or more. Change each 1 000 into a kilometre and carry it over.
In subtraction there may not be enough metres. Borrow one kilometre and turn it into 1 000 m.
d) Multiplying and dividing
Multiply or divide each part, then tidy up.
Three journeys of 4 km 500 m come to 12 km 1 500 m. Change the 1 500 m, giving 13 km 500 m.
Split a road of 6 km 400 m into 4 equal parts. Each part is 1 km 600 m.
e) Estimating distance
| Distance | About |
|---|---|
| Across a classroom | 8 m |
| A football pitch | 100 m |
| Ten minutes walking | 1 km |
| Nairobi to Thika | 45 km |
Guess before you calculate. If you expect about 3 km and get 300 km, check your work.
f) Where this is used
A driver reads distance signs. A runner measures a race. A farmer walks the edge of a field. Anyone planning a journey works in kilometres.
:::checkpoint Check yourself
- How many metres make one kilometre?
- Change 8 km into metres.
- Change 2 400 m into kilometres and metres.
- Add 3 km 800 m and 2 km 400 m. :::
Definitions
- Kilometre (km) — a unit of length equal to 1,000 metres.
- Metre (m) — the base unit of length.
Must Remember
- 1 km = 1,000 m.
- Convert mixed km/m amounts to metres before calculating.
- Convert the final answer back to km and m if needed.
- Multiply to convert km to m; divide to convert m to km.
Conclusion
Convert to metres first, calculate, then convert back if needed — the same pattern for every calculation in this topic.