 # What is 7/8 + 9/12? Let's add

 7 8
+
 9 12

## Step 1

We can't add two fractions with different denominators (the bottom number). So you need to get a common denominator - both bottom numbers need to match. 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 7 by 12, and get 84, then we multiply 8 by 12 and get 96. Do the same for the second term. We multiply 9 by 8, and get 72, then multiply 8 by 12 and get 96. So now our fractions look like this:

 84 96
+
 72 96

## Step 2

Since our denominators match, we can add the numerators.

84 + 72 = 156

Now we have an answer.

 156 96

## 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:

 156 96
÷ 2 =
 78 48

Let's try dividing by that again...

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

 78 48
÷ 2 =
 39 24

Let's try dividing by that 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:

 39 24
÷ 3 =
 13 8

Let's try dividing by that again...

Nope! So now we try the next greatest prime number, 5...

Nope! So now we try the next greatest prime number, 7...

Nope! So now we try the next greatest prime number, 11...

No good. 11 is larger than 8. So we're done reducing.

There you have it! Here's the final answer to 7/8 + 9/12

 7 8
+
 9 12
=
 13 8
© 2014 Randy Tayler