2
Grams, kilograms and tonnes
Discover Mathematics P4: Term 1, Unit 3, Lessons 1–4
GoalChoose between g, kg and tonne to measure mass, and change between them.
New words
mass · how much matter is in an object; we weigh it to measure itgram (g) · a small unit of masskilogram (kg) · 1 kg = 1,000 gtonne (t) · 1 t = 1,000 kg, for very heavy things
Explanation
We measure how heavy things are with units of mass. For small things we use grams: an egg is about 60 g. For school bags, fruit and people we use kilograms: a bag is about 4 kg. For trucks and big loads we use tonnes: a small truck can carry 3 t. The links are 1 kg = 1,000 g and 1 t = 1,000 kg. To change kg to g, multiply by 1,000: 2 kg 920 g = 2 × 1,000 + 920 = 2,920 g. To change g to kg, divide by 1,000: 5,400 g = 5 kg 400 g. And 3 t = 3,000 kg. A balance is level when the two sides have equal mass, so 2 kg 500 g balances 2,500 g.
Worked examples
| Object | Mass | Unit |
|---|---|---|
| egg | 60 | g |
| schoolbag | 4 | kg |
| truck load | 3 | t |
| From | To |
|---|---|
| 2 kg 920 g | 2,920 g |
| 5,400 g | 5 kg 400 g |
| 3 t | 3,000 kg |
Mariam buys 1 kg 250 g of tomatoes and 750 g of cucumbers. Together: 1,250 + 750 = 2,000 g, which is 2 kg. The cucumbers are 1,250 − 750 = 500 g lighter.
Class activity
Kitchen scale. Weigh five things from the kitchen on a scale: sugar, rice, an apple, a tomato and a bag of tea. Write each mass in grams and then in kg and g. Which two together weigh about 1 kg?
Practice
1
Which unit is best for the mass of a lorry: g, kg or t?
Tonnes (t).
2
Change 4 kg 50 g to grams.
4 × 1,000 + 50 = 4,050 g.
3
Change 7,300 g to kg and g.
7 kg 300 g.
4
A sack of flour has a mass of 25 kg. How many grams is that?
25 × 1,000 = 25,000 g.
5
Karim says 6 t = 600 kg. What is his mistake? Give the right answer.
1 t = 1,000 kg, not 100 kg. So 6 t = 6,000 kg.