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When we subtract 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
| 5 | - | 5 |
| 6 | 9 |
Answer
We must first find the lowest common multiple of 6 and 9, which is 18.
Then we change each fraction into 18ths.
18 ÷ 6 = 3 so we multiply the top and bottom of the first fraction by 3.
18 ÷ 9 = 2 so we multiply the top and bottom of the second fraction by 2.
| 5 | - | 5 |
| 6 | 9 |
| = | 5 x 3 | - | 5 x 2 |
| 6 x 3 | 9 x 2 |
| = | 15 | - | 10 |
| 18 | 18 |
| = | 5 |
| 18 |
Let's have a go at some questions now.
