Mass

CBC Grade 5 Mathematics — Mass

Lesson Objectives

By the end of this topic, a learner should be able to:

• Identify the gramme as a unit for measuring mass
• Explain the relationship between kilogrammes and grammes
• Convert between kilogrammes and grammes
• Add, subtract, multiply, and divide masses given in kilogrammes and grammes
• Appreciate the use of kilogrammes and grammes in everyday situations

Mass

Mass is how heavy something is. You already know the kilogramme. Grade 5 adds the gramme, for light things.

a) The gramme

A gramme is a very small mass. The short way to write it is g.

A single sweet is about 5 g. A pencil is about 10 g.

1 kilogramme = 1 000 grammes.

b) Everyday masses

Thing	About
A sweet	5 g
A pencil	10 g
A packet of biscuits	200 g
A loaf of bread	500 g
A packet of sugar	1 kg
A bag of cement	50 kg

Guess before you calculate. If you expect about 2 kg and get 200 kg, check your work.

c) Converting

To change kilogrammes to grammes, multiply by 1 000.

To change grammes to kilogrammes, divide by 1 000.

A check: grammes are smaller, so there are more of them.

d) Adding

Add the grammes first, then the kilogrammes.

The grammes may come to 1 000 or more. Change each 1 000 into a kilogramme and carry it over.

Add 2 kg 600 g and 1 kg 700 g. That gives 3 kg 1 300 g, which becomes 4 kg 300 g.

e) Subtracting

If there are not enough grammes to take from, borrow one kilogramme.

That kilogramme becomes 1 000 grammes. Add it to the grammes you already have.

Remember to reduce the kilogrammes by one after borrowing.

f) Multiplying and dividing

Multiply or divide each part, then tidy up.

Four packets of 1 kg 250 g weigh 4 kg 1 000 g. That is 5 kg exactly.

A 6 kg bag shared into 4 equal parts gives 1 kg 500 g each.

g) Using a weighing scale

Put the scale on a flat surface.

Check it reads zero before you start. If it does not, set it back to zero.

Read the mark where the pointer stops, at eye level.

h) Where this is used

Buying sugar or flour. Weighing a baby at the clinic. Posting a parcel. Selling produce at a market.

:::checkpoint Check yourself

1. How many grammes make one kilogramme?
2. Change 6 kg into grammes.
3. Change 3 800 g into kilogrammes and grammes.
4. Take 1 kg 600 g from 4 kg 300 g. :::

Definitions

• Kilogramme (kg) — a unit of mass equal to 1,000 grammes.
• Gramme (g) — the base unit of mass.

Must Remember

1. 1 kg = 1,000 g.
2. Convert mixed kg/g amounts to grammes before calculating.
3. Convert the final answer back to kg and g if needed.
4. Multiply to convert kg to g; divide to convert g to kg.

Conclusion

Same pattern as Length and Capacity: convert to the smaller unit, calculate, then convert back.