To make a fraction into a decimal is more simple than vise versa. To change it, you simply divide the numerator to the denominator. 
     For example, if you have the fraction 1/3, you would divide 1 into 3, giving you .33 (repeating decimal). This is pretty much it, but because I need to type more, how about some more examples?
     Oh, also, you need to have the fraction in simplest form. So, you can't work with 9/18, you would work with 1/2. 1/2 is a simple decimal, and everyone knows that. It is .5 because 1 divided by 2 is .50, but you can drop the zero. All it does is hold up unnecessary space. Bad zero. Anyway, a third example...how about a more complex one? 70/83. You divide 70 into 83. This gives you 0.84.

     Lets say you're a restaurant owner and you're buying food for your business. Would it be better to use a percent or ratio to figure out how much you need to buy?