math help

What is 3/18 + 5/12?

What is 3/18 + 5/12?

This is how we add

3
18
+
5
12

Step 1

Of course, you can't add two fractions if the denominators (bottom numbers) don't match. To get a common denominator, multiply the denominators together. Then we fix the numerators by multiplying each one by their other term's denominator.

Now you multiply 3 by 12, and get 36, then we multiply 18 by 12 and get 216.

3/18 times 12

Do the same for the second term. We multiply 5 by 18, and get 90, then multiply 18 by 12 and get 216.

5/12 times 18

The problem now has new fractions to add:

36
216
+
90
216

Step 2

Since our denominators match, we can add the numerators.

36 + 90 = 126

The sum we get is

126
216

Step 3

The last step is to reduce the fraction if we can.

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

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

126
216
÷ 2 =
63
108

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...

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

63
108
÷ 3 =
21
36

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

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

21
36
÷ 3 =
7
12

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 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. 11 is larger than 7. So we're done reducing.

And we're done! Here's the final answer to 3/18 + 5/12

3
18
+
5
12
=
7
12
© 2014 Randy Tayler