What is 9/12 - 9/10?

Here's how to subtract 9/10 from 9/12:

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 10, and get 90.

Then we multiply 9 by 12, and get 108.

Next we give both terms new denominators -- 12 × 10 = 120.

So now our fractions look like this:

Step 2

Since our denominators match, we can subtract the numerators.

90 − 108 = -18

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...

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:

Let's try dividing by 3 again...

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

No good. 5 is larger than -3. So we're done reducing.