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When we add or 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
Simplify:
| a | + | 5c |
| 3b | 6d |
Answer
We must first find a common multiple of 3b and 6d, which is 6bd.
Then we change each fraction into '6bd' ths.
We multiply top and bottom of the first fraction by 2d.
We multiply top and bottom of the second fraction by b.
| a | + | 5c |
| 3b | 6d |
| = | a x 2d | + | 5c x b |
| 3b x 2d | 6d x b |
| = | 2ad | + | 5bc |
| 6bd | 6bd |
| = | 2ad + 5bc |
| 6bd |
Let's tackle some questions now.
