math help

What is 78/10 + 4/9?

What is 78/10 + 4/9?

This is how we add

78
10
+
4
9

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 9, and get 702, then we multiply 10 by 9 and get 90.

78/10 times 9

Now for the second term. You multiply 4 by 10, and get 40, then multiply 10 by 9 and get 90.

4/9 times 10

This gives us a new problem that looks like so:

702
90
+
40
90

Step 2

Since our denominators match, we can add the numerators.

702 + 40 = 742

So what's the answer so far?

742
90

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:

742
90
÷ 2 =
371
45

So far so good... let's try to divide by that number again.

No good. So next you try the next prime number, which is 3...

No good. So next you try the next prime number, which is 5...

No good. So next you try the next prime number, which is 7...

No good. So next you try the next prime number, which is 11...

No good. So next you try the next prime number, which is 13...

No good. So next you try the next prime number, which is 17...

No good. So next you try the next prime number, which is 19...

No good. So next you try the next prime number, which is 23...

No good. So next you try the next prime number, which is 29...

No good. So next you try the next prime number, which is 31...

No good. So next you try the next prime number, which is 37...

No good. So next you try the next prime number, which is 41...

No good. So next you try the next prime number, which is 43...

No good. So next you try the next prime number, which is 47...

No good. 47 is larger than 45. So we're done reducing.

And we're done! Here's the final answer to 78/10 + 4/9

78
10
+
4
9
=
371
45
© 2014 Randy Tayler