math help

What is 21/63 + 8/11?

What is 21/63 + 8/11?

Here's how you add

21
63
+
8
11

Step 1

Can you add yet? Nope! The denominators don't match. We need a common denominator. So next we take both denominators and multiply them. Next, take each numerator and multiply it by the denominator of the other term.

So, we multiply 21 by 11, and get 231, then we multiply 63 by 11 and get 693.

21/63 times 11

Now for the second term. You multiply 8 by 63, and get 504, then multiply 63 by 11 and get 693.

8/11 times 63

We now have a new problem, that looks like this:

231
693
+
504
693

Step 2

Since our denominators match, we can add the numerators.

231 + 504 = 735

That gives us the sum, which is

735
693

Step 3

Now, do we need to simplify this fraction?

First, we attempt to divide 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:

735
693
÷ 3 =
245
231

Now, try the same number again.

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

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

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

245
231
÷ 7 =
35
33

Now, try the same number again.

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 35. So we're done reducing.

Congratulations! Here's your final answer to 21/63 + 8/11

21
63
+
8
11
=
35
33
© 2014 Randy Tayler