Primary 4 maths · Fractions · About 10 minutes
Find a fraction of a set
Identify the amount that acts as the whole, then one part, then the selected parts.
Start the interactive lesson →Open practice activity
What you will learn
- Find a fraction of a set
Models used: number sentences, stories, tables.
Before you start
Find a fraction of a group
Here are 12 counters. We want two thirds of them.
Each dot stands for one object. A full row holds five; two full rows make ten.
Here are 12 counters. We want two thirds of them.
The denominator determines one part’s size. The numerator tells us how many of those parts to take.
There are 3 groups, with 4 objects in each group. Count a group before counting them all.
Thirds means three equal groups. Each group has 4 counters.
4 + 4 + 4 = 3 × 4 = 12
There are 2 groups, with 4 objects in each group. Count a group before counting them all.
Keep two of those groups. Two groups of four make eight.
2/3 of 12 = 8
4 + 4 = 2 × 4 = 8
What did the picture help us see?
Keep two of those groups. Two groups of four make eight.
Worked example: A new example, together
Find 2/4 of 12.
| Equal groups | In each group | Parts needed |
|---|---|---|
| 4 | 3 | 2 |
Share into denominator-many parts, then select numerator-many. Read each value with the heading above its column.
Identify the amount that acts as the whole, then one part, then the selected parts.
A fraction of a amount scales that quantity by the fraction.
Share into denominator-many parts, then select numerator-many Equal groups In each group Parts needed 4 3 2 Share into denominator-many parts, then select numerator-many. Read each value with the heading above its column.
A fraction of an amount means divide by 4, then take 2 of those parts.
Share into denominator-many parts, then select numerator-many Equal groups In each group Parts needed 4 3 2 Find 2/4 of 12.
6
Share into denominator-many parts, then select numerator-many. Read each value with the heading above its column.
A fraction of an amount means divide by 4, then take 2 of those parts.
Share into denominator-many parts, then select numerator-many Equal groups In each group Parts needed 4 3 2 Share into denominator-many parts, then select numerator-many. Read each value with the heading above its column.
12 ÷ 4 × 2.
Share into denominator-many parts, then select numerator-many Equal groups In each group Parts needed 4 3 2 Share into denominator-many parts, then select numerator-many. Read each value with the heading above its column.
The amount is 6.
Share into denominator-many parts, then select numerator-many Equal groups In each group Parts needed 4 3 2 Share into denominator-many parts, then select numerator-many. Read each value with the heading above its column.
Check the result against the question we started with.
The selected amount divided by 12 equals 2/4.
We found 6. A fraction of a amount scales that quantity by the fraction.
Share into denominator-many parts, then select numerator-many Equal groups In each group Parts needed 4 3 2
Common mistakes to discuss
- Dividing by the numerator. Divide by the denominator to find one part, then take as many as the numerator asks. 2/3 of 12 is 12 ÷ 3 × 2 = 8.
Check your understanding
- Find a fraction of a set
- explain fraction multiplication as selecting a share of an amount
- check the answer against the original quantities and units
Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.
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