What is 7/20 - 3/8?

Here's how to subtract 3/8 from 7/20:

Step 1

We can't subtract two fractions with different denominators. So you need to get a common denominator. 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 7 by 8, and get 56.

Then we multiply 3 by 20, and get 60.

Next we give both terms new denominators -- 20 × 8 = 160.

So now our fractions look like this:

Step 2

Since our denominators match, we can subtract the numerators.

56 − 60 = -4

So the answer is:

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...

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

Let's try dividing by 2 again...

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

Let's try dividing by 2 again...

No good. 2 is larger than -1. So we're done reducing.