Turning a decimal into a fraction?

[mathimpaired]

How do I do this?

A problem from my math book: Solve the proportion 6/5 = -12/x. I have the answer as 33.75, but the book has the answer as 135/4. Can someone please explain this to me? Thanks. Never mind. I posted the wrong problem. The one I'm having trouble with is posted below.

 

[Gene]

Multiply 33.75 times 4/4 because the book's answer has a denominator of 4.
I don't see how either you or the book got that answer 'cause the correct answer is x=-10

 

[mathimpaired]

You're right. I posted the wrong problem. I did get -10 for that one.

Here's the real problem: 20/45 = 15/x. Sorry.

Thanks.

 

[TchrQbic]

You're right. I posted the wrong problem. I did get -10 for that one.

Here's the real problem: 20/45 = 15/x. Sorry.

Thanks.

When you cross-multiply, you obtain 20x = 15(45)
Dividing by 20, you get x = (15*45)/20
Cancelling 5 into 15 and 20 gets you x = [3(45)]/4

This is equivalent to your answer. However, you will often find answers left as improper fractions, rather than converted to decimal form.