Ratios

[p_gorsky]

on pg. 244 of the Official GRE Guide #10 asks if the ration of 2x to 5y is 3 to 4, what is the ratio of x to y? If we cross multiply we get 8x:15y. The answer says 15 to 8. Is there a reason I have this backwards or is it a typo in the book?

[gmbd97]

HI, so according to your question,
2x/5y=3/4
MIND it we are asked to find the RATIO of x and y, that is x/y?
so if we cross multiply the numbers except x and y, we get,
x/y=15:8 (that is the answer!!)

[tommywallach]

Hey Pgorsky,

Did that explanation make sense? I think the problem was that you didn't write it as an equation, which you must do. So in the original question, translate "is" as "equals":

2x/5y = 3/4

Now cross multiply:

8x = 15y

Now divide both sides by y:

8x/y = 15

Now divide both sides by 8:

x/y = 15/8

Make sense?

-t

[p_gorsky]

The second explanation helped a lot. Thanks!

[tommywallach]

Glad to help!

-t