This activity is about adding and subtracting fractions with different denominators.

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**Example**

When adding or subtracting fractions we begin by finding the lowest common multiple **(LCM)** of both **denominators.**

Solve** 15/24 - 8/15**

First, find the **LCM** of the denominators which are 24 and 15.

24 |
48 |
72 |
96 |
120 |
||||

15 |
30 |
45 |
60 |
75 |
90 |
105 |
120 |
... |

The LCM is 120.

We multiplied 24 by **5** to get 120

and

We multiplied 15 by 8 to get 120

Ok, so now we know that the LCM of the denominators is 120, we need to turn our attention to the numerators in this sum.

We must multiply the numerator by the same number as we did by the denominator to find the LCM.

So, we multiply 15 by 5, and 8 by 8.

And, now we're ready to work out the answer...

15 |
- |
8 |
= |
15 x 5 |
- |
8 x 8 |
= |
75 - 64 |
= |
11 |

24 |
15 |
24 x 5 |
15 x 8 |
120 |
120 |

Answers in this activity should be given as reduced fractions.

Ready to give this a go?