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Each week we'll be posting several questions from The Official Guide for GMAT® Review, 13th Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution.

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Since t = 11 seconds represents time, one can immediately eliminate answers C,D and E, because they don't have units of time. (C) x/(ty) has units of 1/time (D) t/(xy) has units of time/speed squared, which finally is time cubed/distance squared (E) xy/t has units of speed squared/time, which finally is distance squared/time cubed

To choose between (A) and (B), we should keep in mind that time is distance/speed. Since the distance in our case is x, it should appear in the numerator.

Hence, Answer A.
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PhD in Applied Mathematics Love GMAT Quant questions and running.

Re: If Juan takes 11 seconds to run y yards, how many seconds [#permalink]

Show Tags

14 Feb 2015, 10:47

pacifist85 wrote:

This was an easy one, but I do have a questions concerning rates.

When is it that we HAVE to find the rate at which 1 unit of work is done, in order to calculate another rate?

I hope my question is understandable...

Thank you, Natalia

If you construct a table which is like the one given below it will be clear to you what you have been given and what you need to find out what is asked. For this question, R * T = D ? * 11 = y

and we need to find out

R * T = D ? * ? = x you need the rate here to find out the time.That as specified by the question is the same as the first case. So R=y/11. So time=x/(y/11)=11x/y.

This problem is testing us on the Rate x Time = Distance relationship. This relationship also tells us that Rate = Distance/Time and Time = Distance/Rate.

Ultimately, we are looking for how many seconds it will take Juan to run x yards. Thus, the equation we’ll use is: Time = Distance/Rate. We know the distance is x yards, and we need to find Juan’s rate.

We can find Juan’s rate as follows: Rate = Distance/Time = y yards/11 seconds

Using that rate, we need to determine how long it takes him to run x yards at the same rate. So we have:

Time = Distance/Rate

Time = x yards/(y yards/11 seconds)

Time = (x yards) x (11 seconds/y yards)

Time = 11x/y seconds

Answer A.
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