What is 21/63 + 9/12?

Here's how to add

Step 1

We still have different denominators (bottom numbers), though, so we need to get a common denominator. This will make the bottom numbers match. Multiply the denominators together first. Now, multiply each numerator by the other term's denominator.

Now we multiply 21 by 12, and get 252, then we multiply 63 by 12 and get 756.

Now for the second term. You multiply 9 by 63, and get 567, then multiply 63 by 12 and get 756.

This gives us a new problem that looks like so:

Step 2

Since our denominators match, we can add the numerators.

252 + 567 = 819

That gives us an answer of

Step 3

Can this fraction be reduced?

First, we attempt to divide 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:

Let's try dividing by that again...

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

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...

Are both the numerator and the denominator evenly divisible by 7? Yes! So we reduce it:

Let's try dividing by that again...

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 12. So we're done reducing.

There you have it! Here's the final answer to 21/63 + 9/12