 # What is 3/12 + 6/9? This is how you add

 3 12
+
 6 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 3 by 9, and get 27, then we multiply 12 by 9 and get 108. Do the same for the second term. We multiply 6 by 12, and get 72, then multiply 12 by 9 and get 108. The problem now has new fractions to add:

 27 108
+
 72 108

## Step 2

Since our denominators match, we can add the numerators.

27 + 72 = 99

The sum we get is

 99 108

## Step 3

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

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

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:

 99 108
÷ 3 =
 33 36

Let's try dividing by that again...

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

 33 36
÷ 3 =
 11 12

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...

Nope! So now we try the next greatest prime number, 13...

No good. 13 is larger than 11. So we're done reducing.

There you have it! Here's the final answer to 3/12 + 6/9

 3 12
+
 6 9
=
 11 12
© 2014 Randy Tayler