What is 9/10 - 8/9?

Here's how to subtract 8/9 from 9/10:

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 9 by 9, and get 81.

Then we multiply 8 by 10, and get 80.

Next we give both terms new denominators -- 10 × 9 = 90.

So now our fractions look like this:

Step 2

Since our denominators match, we can subtract the numerators.

81 − 80 = 1

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...

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