PHP convert decimal into fraction and back?

Question

I want the user to be able to type in a fraction like:

 1/2
 2 1/4
 3

And convert it into its corresponding decimal, to be saved in MySQL,

Answer 1

An approach would be to retrieve the decimal value and multiply it by 2, 3, 4 and so on until you get an integer number.

However, I'd stick with the answer given by Derek. Guess what happens when a user inserts n/(n+1) with n high. Such an algorithm would have to scan all the numbers up to n+1. Not to mention it is likely you'll end up with approximation problems.