math help

What is 78/10 + 9/12?

What is 78/10 + 9/12?

Here's how we add

78
10
+
9
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 78 by 12, and get 936, then we multiply 10 by 12 and get 120.

78/10 times 12

Now for the second term. You multiply 9 by 10, and get 90, then multiply 10 by 12 and get 120.

9/12 times 10

This gives us a new problem that looks like so:

936
120
+
90
120

Step 2

Since our denominators match, we can add the numerators.

936 + 90 = 1026

So what's the answer so far?

1026
120

Step 3

Can this fraction be reduced?

First, we attempt to divide it by 2...

Are both the numerator and the denominator evenly divisible by 2? Yes! So we reduce it:

1026
120
÷ 2 =
513
60

Now, try the same number again.

Nope. Try the next prime number, 3...

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

513
60
÷ 3 =
171
20

Now, try the same number again.

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

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

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...

No good. 23 is larger than 20. So we're done reducing.

Congratulations! Here's your final answer to 78/10 + 9/12

78
10
+
9
12
=
171
20
© 2014 Randy Tayler