math help

What is 21/63 + 3/12?

What is 21/63 + 3/12?

Let's add

21
63
+
3
12

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

21/63 times 12

Now for the second term. You multiply 3 by 63, and get 189, then multiply 63 by 12 and get 756.

3/12 times 63

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

252
756
+
189
756

Step 2

Since our denominators match, we can add the numerators.

252 + 189 = 441

Answer:

441
756

Step 3

Now, do we need to simplify this fraction?

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:

441
756
÷ 3 =
147
252

Let's try dividing by that again...

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

147
252
÷ 3 =
49
84

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:

49
84
÷ 7 =
7
12

Let's try dividing by that again...

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

No good. 11 is larger than 7. So we're done reducing.

There you have it! Here's the final answer to 21/63 + 3/12

21
63
+
3
12
=
7
12
© 2014 Randy Tayler