 # What is 8/12 - 3/9? Here's how to subtract 3/9 from 8/12:

 8 12
 3 9

## Step 1

We can't subtract two fractions with different denominators. So you need to get a common denominator. To do this, you'll multiply the denominators times each other... but the numerators have to change, too. They get multiplied by the other term's denominator.

So we multiply 8 by 9, and get 72.

Then we multiply 3 by 12, and get 36.

Next we give both terms new denominators -- 12 × 9 = 108.

So now our fractions look like this:

 72 108
 36 108

## Step 2

Since our denominators match, we can subtract the numerators.

72 − 36 = 36

 36 108

## Step 3

Last of all, we need to simplify the fraction, if possible. Can it be reduced to a simpler fraction?

To find out, we try dividing it by 2...

Are both the numerator and the denominator evenly divisible by 2? Yes! So we reduce it:

 36 108
÷ 2 =
 18 54

Let's try dividing by 2 again...

Are both the numerator and the denominator evenly divisible by 2? Yes! So we reduce it:

 18 54
÷ 2 =
 9 27

Let's try dividing by 2 again...

Nope! So now we try the next greatest prime number, 3...

Are both the numerator and the denominator evenly divisible by 3? Yes! So we reduce it:

 9 27
÷ 3 =
 3 9

Let's try dividing by 3 again...

Are both the numerator and the denominator evenly divisible by 3? Yes! So we reduce it:

 3 9
÷ 3 =
 1 3

Let's try dividing by 3 again...

No good. 3 is larger than 1. So we're done reducing.

There you have it! The final answer is:
 8 12
 3 9
=
 1 3