# If subtracting is your aim

If adding or subtracting is your aim,

the bottom numbers must be the same

And to put all the fractions with the same bottom number you must:

Multiply the top and bottom of each fraction by

the other fraction's bottom number

Note: There are many ways to subtract fractions but with Mammoth Memory, we propose this one method that suits every subtraction of a fraction. That way you only have one rhyming slogan to remember.

**Example 1**

`5/9-1/9=(5-1)/9=4/9`

In this example, the bottom numbers (denominators) are the same.

**Example 2**

`5/6-3/8`

Make the bottom denominator the same for both so multiply the top and bottom of each fraction by the other fraction's denominator.

`5/6\times8/8-3/8\times6/6`

**NOTE:**

`6/6\ or8/8=1`

When multiplying by 1 it does not alter the fraction.

Therefore

`5/6\times8/8=(5\times8)/(6times8)=40/48`

and

`3/8\times6/6=(3\times6)/(8times6)=18/48`

So subtract fractions

`40/48\-18/48=(40\-18)/(48)=22/48`

Now just make `22/48` simpler

`22/48=11/24`

**Example 3**

Work out `3/4-1/6`

Make the bottom denominator the same for both so multiply the top and bottom of each fraction by the other fraction's denominator.

`3/4\times6/6-1/6\times4/4`

**NOTE:**

`6/6\ or4/4=1`

When multiplying by 1 it does not alter the fraction.

Therefore

`3/4\times6/6=(3\times6)/(4times6)=18/24`

and

`1/6\times4/4=(1\times4)/(6times4)=4/24`

subtract fractions

`18/24\-4/24=(18\-4)/(24)=14/24`

Now just make `14/24` simpler

`14/24=7/12`