What is 8/9 - 9/10?

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

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 8 by 10, and get 80.

Then we multiply 9 by 9, and get 81.

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

So now our fractions look like this:

Step 2

Since our denominators match, we can subtract the numerators.

80 − 81 = -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.