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In this worksheet, students add two simple fractions by first finding their lowest common denominator.

Key stage:  KS 3

Curriculum topic:   Number

Curriculum subtopic:   Use Four Operations for All Numbers

Difficulty level:

### QUESTION 1 of 10

When we add two fractions, they must have the same denominator.

We use equivalent fractions to change them into two fractions with the same lowest common denominator.

Example

Work out

 3 + 1 10 15

We must first find the lowest common multiple of 10 and 15, which is 30.

Then we change each fraction into 30ths.

30 ÷ 10 = 3 so we multiply top and bottom of the first fraction by 3.

30 ÷ 15 = 2 so we multiply top and bottom of the second fraction by 2.

 3 + 1 10 15

 = 3 × 3 + 1 × 2 10 × 3 15 × 2

 = 9 + 2 30 30

 = 11 30

Work out

 2 + 1 3 4

Work out

 2 + 1 3 5

Work out

 2 + 1 5 3

Work out

 2 + 1 5 4

Work out

 3 + 1 5 6

Work out

 2 + 1 5 10

Work out

 2 + 1 7 4

Work out

 2 + 3 9 4

Work out

 2 + 1 9 6

Work out

 5 + 1 6 9

• Question 1

Work out

 2 + 1 3 4

11/12
• Question 2

Work out

 2 + 1 3 5

13/15
• Question 3

Work out

 2 + 1 5 3

11/15
• Question 4

Work out

 2 + 1 5 4

13/20
• Question 5

Work out

 3 + 1 5 6

23/30
• Question 6

Work out

 2 + 1 5 10

1/2
• Question 7

Work out

 2 + 1 7 4

15/28
• Question 8

Work out

 2 + 3 9 4

35/36
• Question 9

Work out

 2 + 1 9 6

7/18
• Question 10

Work out

 5 + 1 6 9

17/18
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