math help

What is 21/33 + 3/12?

What is 21/33 + 3/12?

This is how to add

21
33
+
3
12

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 33 by 12 and get 396.

21/33 times 12

Now for the second term. You multiply 3 by 33, and get 99, then multiply 33 by 12 and get 396.

3/12 times 33

This gives us a new problem that looks like so:

252
396
+
99
396

Step 2

Since our denominators match, we can add the numerators.

252 + 99 = 351

So what's the answer so far?

351
396

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:

351
396
÷ 3 =
117
132

Let's try dividing by that again...

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

117
132
÷ 3 =
39
44

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...

Nope! So now we try the next greatest prime number, 17...

Nope! So now we try the next greatest prime number, 19...

Nope! So now we try the next greatest prime number, 23...

Nope! So now we try the next greatest prime number, 29...

Nope! So now we try the next greatest prime number, 31...

Nope! So now we try the next greatest prime number, 37...

Nope! So now we try the next greatest prime number, 41...

No good. 41 is larger than 39. So we're done reducing.

There you have it! Here's the final answer to 21/33 + 3/12

21
33
+
3
12
=
39
44
© 2014 Randy Tayler