math help

What is 15/60 + 4/7?

What is 15/60 + 4/7?

This is how you add

15
60
+
4
7

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 15 by 7, and get 105, then we multiply 60 by 7 and get 420.

15/60 times 7

Do the same for the second term. We multiply 4 by 60, and get 240, then multiply 60 by 7 and get 420.

4/7 times 60

The problem now has new fractions to add:

105
420
+
240
420

Step 2

Since our denominators match, we can add the numerators.

105 + 240 = 345

The sum we get is

345
420

Step 3

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

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

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:

345
420
÷ 3 =
115
140

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...

Are both the numerator and the denominator evenly divisible by 5? Yes! So we reduce it:

115
140
÷ 5 =
23
28

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 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. 29 is larger than 23. So we're done reducing.

And we're done! Here's the final answer to 15/60 + 4/7

15
60
+
4
7
=
23
28
© 2014 Randy Tayler