Mass Measurements
Primary 4 · Mathematics
Mass Measurements
Lesson 2 of 4
20 min
Let's begin
A lorry arrives at a tea factory near Nyungwe forest. It carries 3 tonnes of green tea leaves.
At the same time, at the health centre, a nurse gives Byiringiro a tablet. The box says 500 mg.
Tonnes and milligrams! One is enormous and one is tiny. Today you will meet all the units of mass and learn to change from one to another.
From the kilogram down to the milligram there are seven units. Each unit is 10 times the unit just below it, like the capacity ladder.
1 tonne (t) = 1 000 kg. Lorry loads, harvests and big animals are measured in tonnes.
Farmers sometimes sell harvests by the quintal (q). 1 q = 100 kg, so 10 q make 1 t.
| Unit | Use it for |
|---|---|
| tonne (t) | a lorry of sand, a harvest of maize |
| kilogram (kg) | people, goats, sacks of rice |
| gram (g) | fruit, bread, a packet of tea |
| milligram (mg) | medicine tablets |
Worked example 1
4 kg = ? g. From kg to g is 3 steps, so × 1 000. 4 × 1 000 = 4 000 g.
Worked example 2
3 t = ? kg. 1 t = 1 000 kg, so 3 × 1 000 = 3 000 kg.
Worked example 3
6 hg = ? g. From hg to g is 2 steps, so × 100. 6 × 100 = 600 g.
Worked example 4
2 500 g = ? kg. 2 500 ÷ 1 000 = 2.5 kg, which is 2 kg 500 g.
Worked example 5
750 g = ? kg. 750 ÷ 1 000 = 0.75 kg.
Worked example 6
500 mg = ? g. 500 ÷ 1 000 = 0.5 g. So Byiringiro's tablet is half a gram.
3 kg 250 g = 3 000 g + 250 g = 3 250 g.
Careful! 5 kg 80 g = 5 080 g, not 5 800 g. There are no hundreds of grams, so write a 0 in that place.
Tip
Kilo means a thousand. 1 kilogram = 1 000 grams, 1 kilolitre = 1 000 litres, 1 kilometre = 1 000 metres. And 1 000 milligrams make 1 gram.
Work each one in your exercise book first. Then tap Show answer to check.
6 kg = ___ g
Answer: 6 000 g, because 6 × 1 000 = 6 000.
9 000 g = ___ kg
Answer: 9 kg, because 9 000 ÷ 1 000 = 9.
2 t = ___ kg
Answer: 2 000 kg, because 1 t = 1 000 kg.
3 kg 250 g = ___ g
Answer: 3 250 g. 3 000 g + 250 g = 3 250 g.
1 500 mg = ___ g
Answer: 1.5 g, because 1 500 ÷ 1 000 = 1.5.
What you learned today
Sources and credits
The full mass ladder from tonne to milligram, the stories, Rwandan examples, drawings and practice questions were written by Ganzaa.
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