A fraction of a set

Primary 5 Four Operations of Fractions study guide: the whole chapter, step by step

About this subtopic

A fraction of a set is in the Primary 5 Four Operations of Fractions chapter. The lesson film below teaches it with its own questions, and the practice set is written for Primary 5.

Lesson video, with the working

The bottom number makes the groups

2 min 38 s

The film teaches 2 questions in turn. Each question shows first; its working is written as the film explains it.

Watch on its own page

Today's question

A box holds 30 eggs. 2/5 of the eggs are brown. How many of the eggs are brown?

  1. 12 eggs are brown.

Ans: 12

Example 1

The same box holds 30 eggs. 3/5 of the eggs are white. How many of the eggs are white?

  1. 18 eggs are white.

Ans: 18

How to solve it
  1. Look at the bottom number, 5. Split the 30 eggs into 5 equal groups.
  2. Find one group: 30 split into 5 equal groups is 6 eggs.
  3. Look at the top number, 2. Take 2 of the 5 groups.
  4. 2 groups of 6 eggs is 12 eggs, so 12 eggs are brown.
  5. The same answer from 2 fifths times 30: 5 goes into 30 six times, so it is 2 times 6, which is 12.

The bottom number makes the equal groups. The top number says how many groups to take.

Practice questions with worked solutions

Question 1 is free to try, each with its full working.

Intermediate

1Free
Question 1 of 1 · Intermediate · free to tryThere are 84 chairs in a hall. 5/7 are blue and the rest are white. How many…There are 84 chairs in a hall…

There are 84 chairs in a hall. 5/7 are blue and the rest are white. How many more blue chairs than white chairs are there?

Show the working and the answer

Video solution · 1 min 30 s

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Working

  1. blue chairs = 5 units; white chairs = 7 − 5 = 2 units
  2. difference = 5 − 2 = 3 units
  3. 1 unit = 84 ÷ 7 = 12
  4. 3 units = 3 × 12 = 36

Answer: 36

For parents

How do you solve fraction of a set questions in P5?

A fraction of a set takes part of a group of objects, such as 2/5 of 30 eggs.

What your child learns here

A fraction of a set takes part of a group of objects, such as 2/5 of 30 eggs. This page uses the Primary 5 outcome of multiplying a proper fraction and a whole number, and shows it both as equal groups and as a bar cut into units.

  • The denominator tells how many equal groups to split the set into.
  • Divide the number of objects in the set by the denominator to find one group.
  • The numerator tells how many groups to take, so multiply one group by it.
  • The rest of the set is the other groups: seven sevenths minus five sevenths leaves two sevenths.
  • The same answer comes from the fraction times the whole number, for example 2/5 × 30 = 12.
Does the answer make sense?

One unit is 84 divided by 7, which is 12 chairs. The blue chairs are 5 units, or 60, and the white chairs are 2 units, or 24, and 60 plus 24 gives back the 84 chairs. The answer of 36 is 3 units, less than the 60 blue chairs, as a 'how many more' answer has to be.

How to practise these questions

This page has one practice question for now, and it is free: a hall has 84 chairs, 5/7 of them are blue and the rest are white, and your child finds how many more blue chairs there are than white chairs. It is an Intermediate question, because the white chairs must be found as well as the blue ones before the two are compared. If your child is stuck, open its worked solution and draw one bar of 7 equal units for the 84 chairs.

Questions parents ask

What is a fraction of a set? It is a fraction of a group of separate objects rather than of one shape. Three quarters of 20 marbles means 4 equal groups of 5 marbles with 3 groups taken, so 15 marbles.

Which number does my child divide by? Divide the whole set by the denominator, the bottom number, to get one group, then multiply by the numerator, the top number. Dividing by the top number gives groups of the wrong size.

Is fraction of a set taught in Primary 5? It begins in Primary 4. Primary 5 adds multiplying a proper fraction and a whole number, the same calculation written as a single multiplication.