math help

What is 15/60 + 5/7?

What is 15/60 + 5/7?

This is how we add

15
60
+
5
7

Step 1

Can you add yet? Nope! The denominators don't match. We need a common denominator. So next we take both denominators and multiply them. Next, take each numerator and multiply it by the denominator of the other term.

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

15/60 times 7

Now for the second term. You multiply 5 by 60, and get 300, then multiply 60 by 7 and get 420.

5/7 times 60

We now have a new problem, that looks like this:

105
420
+
300
420

Step 2

Since our denominators match, we can add the numerators.

105 + 300 = 405

That gives us the sum, which is

405
420

Step 3

Now, do we need to simplify this fraction?

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

Nope! So now we try the next greatest prime number, 3...

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

405
420
÷ 3 =
135
140

Let's try dividing by that again...

Nope! So now we try the next greatest prime number, 5...

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

135
140
÷ 5 =
27
28

Let's try dividing by that again...

Nope! So now we try the next greatest prime number, 7...

Nope! So now we try the next greatest prime number, 11...

Nope! So now we try the next greatest prime number, 13...

Nope! So now we try the next greatest prime number, 17...

Nope! So now we try the next greatest prime number, 19...

Nope! So now we try the next greatest prime number, 23...

Nope! So now we try the next greatest prime number, 29...

No good. 29 is larger than 27. So we're done reducing.

There you have it! Here's the final answer to 15/60 + 5/7

15
60
+
5
7
=
27
28
© 2014 Randy Tayler