Solve 3/x = 9/12

Step by step

The question

Question: solve 3/x = 9/12.

Two fractions are equal.

1 Cross multiply

When two fractions are equal, we can cross multiply.

These two are equal.

Work out the multiplications.

Let's swap the two sides, so x is on the left.

2 Remove the 9

9x means 9 times x.

We want just x.

To remove times 9, we divide by 9.

We do it on both sides.

Why both sides?

The = sign means both sides are the same amount.

If we change only one side, they are not the same any more.

9 divided by 9 is 1.

So just x is left.

36 divided by 9 is 4.

So x = 4!

3 Check

Let's check: put 4 in place of x.

First the left side.

Now the right side.

Both sides are 3/4.

So x = 4 is right!

Let's look back.

First: cross multiply.

Then: remove the 9.

Last: check.