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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]
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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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Re: If Juan takes 11 seconds to run y yards, how many seconds [#permalink]
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24 Feb 2018, 10:53
Hi All,
We're told that it takes Juan 11 seconds to run Y yards. We're asked how many seconds it takes him to run X yards at that same rate. This question can be solved by TESTing VALUES.
IF.... Y = 2 X = 4
Then Juan takes 11 seconds to run 2 yards. At that same rate, he would need 22 seconds to run 4 yards. So we're looking for an answer that = 22 when Y = 2 and X = 4...
Answer A: 11X/Y = 44/2 = 22 This IS a match Answer B: 11Y/X = 22/4 NOT a match Answer C: X/(11Y) = 2/44 NOT a match Answer D: 11/(XY) = 11/8 NOT a match Answer E: (XY)/11 = 8/11 NOT a match
Let's solve the question using the input-output approach.
For example, let's let y = 22 This means that Juan takes 11 seconds to run 22 yards, which means his speed is 2 yards per second.
From here, if we let x = 10, then the question is asking,"how many seconds will it take Juan to run 10 yards at the same rate (of 2 yards per second)?" Well, at that speed, it will take Juan 5 seconds to run 10 yards.
In other words, if we INPUT y = 22 and x = 10, then the answer (the OUTPUT) to the question is 5.
Now we'll plug y = 22 and x = 10 into the answer choices and see which one yields the OUTPUT of 5 (A) 11x/y = (11)(10)/22 = 5 GREAT! (B) 11y/x = (11)(22)/10 = something other than 5 ELIMINATE B (C) x/11y = (10)/(11)(22) = something other than 5 ELIMINATE C (D) 11/xy (11)/(10)(22) = 1/20 ELIMINATE D (E) xy/11 = (10)(22)/(11) = 20 ELIMINATE E
Practice Questions Question: 38 Page: 157 Difficulty: 600
Another option is to use equivalent ratios.
The ratio is time/distance
For every 11 seconds, Juan can run y yards So we get the ratio 11/y
Let T = the time it takes to run x yards. That is, For every T seconds, Juan can run x yards We get the ratio T/x
Since Juan runs at a constant rate, we can write: we get: 11/y = T/x Cross multiply to get: 11x = Ty Divide both sides by y to get: 11x/y = T So, the answer is A
Cheers, Brent
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Re: If Juan takes 11 seconds to run y yards, how many seconds
[#permalink]
28 Apr 2018, 08:20