At the rate of f floors per m minutes, how many floors does an elevato

Looks like a good candidate for the INPUT-OUTPUT approach.

Let's INPUT some values for f, m and s.
Let's say that f = 8 floors, m = 2 minutes, and s = 30 seconds

That is, the elevator travels at a rate of 8 floors per 2 minutes.
How many floors does an elevator travel in 30 seconds?

Well, 8 floors in 2 minutes translates to 4 floors in 1 minute, and 2 floors in 30 seconds.

So, when f = 8, m = 2, and s = 30, the answer to the question (OUTPUT) is 2 floors

Now, let's plug f = 8, m = 2, and s = 30 into each answer choice and see which one yields an OUTPUT of 2

(A) \(\frac{(8)(30)}{60(2)}\) = 2 GREAT!

(B) \(\frac{(2)(30)}{60(8)}\) = 1/8 ELIMINATE

(C) \(\frac{(8)(2)}{(30)}\) = 8/15 ELIMINATE

(D) \(\frac{(8)(30)}{(2)}\) = 120 ELIMINATE

(E) \(\frac{60(30)}{(8)(2)}\) = some big number ELIMINATE

Answer: A

For more information on this question type and this approach, we have some free videos:
- Variables in the Answer Choices - https://www.gmatprepnow.com/module/gmat- ... /video/933
- Tips for the Algebraic Approach - https://www.gmatprepnow.com/module/gmat- ... /video/934
- Tips for the Input-Output Approach - https://www.gmatprepnow.com/module/gmat- ... /video/935

Cheers,
Brent