gmatser1 wrote:

At the rate of f floors per m minutes, how many floors does an elevator travel in s seconds?

(A) \(\frac{fs}{60m}\)

(B) \(\frac{ms}{60f}\)

(C) \(\frac{fm}{s}\)

(D) \(\frac{fs}{m}\)

(E) \(\frac{60s}{fm}\)

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 -

http://www.gmatprepnow.com/module/gmat- ... /video/933 - Tips for the Algebraic Approach -

http://www.gmatprepnow.com/module/gmat- ... /video/934 - Tips for the Input-Output Approach -

http://www.gmatprepnow.com/module/gmat- ... /video/935 Cheers,

Brent

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Brent Hanneson – Founder of gmatprepnow.com