Word Problem Book for GRE - Ratios

[kiricole03]

WP - pg 82 Check Your Skills #6 - I got the ratio 15:20:16. Then you need to find the number of freshmen using the number of juniors given and the ratios. In the solution, the ratio and actual number of juniors are mixed together, 16/240 = 15/x. Is it fine to mix ratios and actual numbers like this or is this an isolated situation? I thought the ratios have to stay together and the actual numbers have to stay together, Ex. If the ratio of apples to oranges is 3:4 and there are 15 apples, then to find the oranges you write 3/4 = 15/x. Here the ratio is on one side of the equal sign and the actual number of oranges and apples is on the other side. I didn't think you could put 3/15 = 4/x. You do get the same answer either way. I just want to make sure that I am setting up problems correctly.

[tommywallach]

Hey Kiri,

The issue isn't which side of the equation you put the ratios or real numbers on, only that the resulting equation is logical.

3/4 = 15/x and 3/15 = 4/x are the same equation (i.e. you get the same result when you solve), so it's really irrelevant what goes where. Just write the equation in whatever way makes sense to you (but let me know if there's some equation that doesn't make sense to you).

-t