 # What is 9/12 + 4/9? 9 12
+
 4 9

## Step 1

Of course, you can't add two fractions if the denominators (bottom numbers) don't match. To get a common denominator, multiply the denominators together. Then we fix the numerators by multiplying each one by their other term's denominator.

Now you multiply 9 by 9, and get 81, then we multiply 12 by 9 and get 108. Do the same for the second term. We multiply 4 by 12, and get 48, then multiply 12 by 9 and get 108. The problem now has new fractions to add:

 81 108
+
 48 108

## Step 2

Since our denominators match, we can add the numerators.

81 + 48 = 129

 129 108

## Step 3

The last step is to reduce the fraction if we can.

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

Nope. Try the next prime number, 3...

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

 129 108
÷ 3 =
 43 36

Now, try the same number again.

Nope. Try the next prime number, 5...

Nope. Try the next prime number, 7...

Nope. Try the next prime number, 11...

Nope. Try the next prime number, 13...

Nope. Try the next prime number, 17...

Nope. Try the next prime number, 19...

Nope. Try the next prime number, 23...

Nope. Try the next prime number, 29...

Nope. Try the next prime number, 31...

Nope. Try the next prime number, 37...

No good. 37 is larger than 36. So we're done reducing.