Loading please wait

The smart way to improve grades

Comprehensive & curriculum aligned

Try an activity or get started for free

Common Denominators

In this worksheet, students use common multiples to express fractions in the same denominators.

'Common Denominators' worksheet

Key stage:  KS 2

Year:  Year 4 11+ worksheets

Curriculum topic:   Maths and Numerical Reasoning

Curriculum subtopic:   Fractions

Difficulty level:  

Worksheet Overview

Before we add or subtract fractions, we try to get them to have the same denominators.

We do this by using lowest common multiples.


Suppose we wish to subtract:

7 - 4
9 6


We look for the smallest number that 9 and 6 go into.

This will be 18, so we change both fractions into 18ths.


We multiply top and bottom of 7 ninths by 2:

7 = 14
9 18


We multiply top and bottom of 4 sixths by 3:

4 = 12
6 18


So we now have:

14 - 12
18 18


The answer is:

2 = 1
18 9




When we work out this calculation, what is the lowest common denominator we should choose for both fractions?

7 - 4
15 10



The lowest common multiple of 15 and 10 is 30, because 2 × 15 = 30 and 3 × 10 = 30.

So the answer is 30.

What is EdPlace?

We're your National Curriculum aligned online education content provider helping each child succeed in English, maths and science from year 1 to GCSE. With an EdPlace account you’ll be able to track and measure progress, helping each child achieve their best. We build confidence and attainment by personalising each child’s learning at a level that suits them.

Get started

Try an activity or get started for free