math help

What is 7/10 - 9/12?

What is 7/10 - 9/12?

Here's how to subtract 9/12 from 7/10:

7
10
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 7 by 12, and get 84.

Then we multiply 9 by 10, and get 90.

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

So now our fractions look like this:

84
120
90
120

Step 2

Since our denominators match, we can subtract the numerators.

84 − 90 = -6

So the answer is:

-6
120

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:

-6
120
÷ 2 =
-3
60

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:

-3
60
÷ 3 =
-1
20

Let's try dividing by 3 again...

No good. 3 is larger than -1. So we're done reducing.

There you have it! The final answer is:
7
10
9
12
=
1
20