What is 1/9 - 1/7?

Here's how to subtract 1/7 from 1/9:

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 1 by 7, and get 7.

Then we multiply 1 by 9, and get 9.

Next we give both terms new denominators -- 9 × 7 = 63.

So now our fractions look like this:

Step 2

Since our denominators match, we can subtract the numerators.

7 − 9 = -2

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...

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

No good. 3 is larger than -2. So we're done reducing.