What is 2/9 + 7/10?

Here's how to add

 2 9
+
 7 10

Step 1

We can't add two fractions with different denominators (the bottom number). So you need to get a common denominator - both bottom numbers need to match. To do this, you'll multiply the denominators times each other... but the numerators have to change, too. They get multiplied by the other term's denominator.

So we multiply 2 by 10, and get 20, then we multiply 9 by 10 and get 90.

Do the same for the second term. We multiply 7 by 9, and get 63, then multiply 9 by 10 and get 90.

So now our fractions look like this:

 20 90
+
 63 90

Step 2

Since our denominators match, we can add the numerators.

20 + 63 = 83

Now we have an answer.

 83 90

Step 3

Last of all, we need to simplify the fraction, if possible. Can it be reduced to a simpler fraction?

To find out, we try dividing it by 2...

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

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...

Nope. Try the next prime number, 29...

Nope. Try the next prime number, 31...

Nope. Try the next prime number, 37...

Nope. Try the next prime number, 41...

Nope. Try the next prime number, 43...

Nope. Try the next prime number, 47...

Nope. Try the next prime number, 53...

Nope. Try the next prime number, 59...

Nope. Try the next prime number, 61...

Nope. Try the next prime number, 67...

Nope. Try the next prime number, 71...

Nope. Try the next prime number, 73...

Nope. Try the next prime number, 79...

Nope. Try the next prime number, 83...

Nope. Try the next prime number, 89...

No good. 89 is larger than 83. So we're done reducing.

Congratulations! Here's your final answer to 2/9 + 7/10

 2 9
+
 7 10
=
 83 90
© 2014 Randy Tayler