Page 48 - Mathematics Coursebook

4.1 Knowing metric units

4.1 Knowing metric units

You can use a tape measure or a ruler to measure distances.

!e metric units of length are the millimetre (mm), centimetre (cm), metre (m) and kilometre (km).
You can use scales to weigh objects.

!e metric units of mass are the gram (g), kilogram (kg) and tonne (t).
You can use a measuring jug to measure how much liquid there is in a container.

!e metric units of capacity are the millilitre (ml) and litre (l).
You need to know these conversion factors.

Units of length Units of mass Units of capacity
ml
500
10 mm = 1 cm 1000 g = 1 kg 1000 ml = 1 l 400
0kg
3.5 0.5 300
100 cm = 1 m 1000 kg = 1 t 3 1 200
1000 m = 1 km 2.5 2 1.5 100

You can convert between di"erent metric units by multiplying or dividing by 10, 100 or 1000.
When you are converting a smaller unit into a bigger one you divide by the conversion factor.
Example: To change metres to kilometres, grams to kilograms or millilitres to litres,
divide by 1000.
When you are converting a bigger unit into a smaller one you multiply by the conversion factor.
Example: To change kilometres to metres, kilograms to grams or litres to millilitres,
multiply by 1000.
When you order decimal numbers that involve measurements, you must make sure all your
measurements are in the same units.

Worked example 4.1
a Convert these measures. i 3.2 km into metres ii 750 g into kilograms
b Write the following lengths in increasing order of size. 50 cm, 0.4 m, 345 mm

a i 1 km = 1000 m The conversion factor is 1000.
3.2 × 1000 = 3200 m You are changing from a bigger unit (km) to a smaller one (m) so multiply
by the conversion factor.
ii 1000 g = 1 kg The conversion factor is 1000.
750 ÷ 1000 = 0.75 kg You are changing from a smaller unit (g) to a bigger one (kg) so divide by
the conversion factor.
b 0.4 m = 40 cm Change the measurements so that they are all in centimetres.
345 mm = 34.5 cm
50 cm, 40 cm, 34.5 cm Rewrite the question with all the lengths in centimetres.
34.5 cm, 40 cm, 50 cm Now compare the lengths and write them in order.
345 mm, 0.4 m, 50 cm Finally write the lengths in the units in which they were given.

4 Length, mass and capacity 4 Length, mass and capacity 47