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Question from GMAC GMAT Review 11th Edition

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Question from GMAC GMAT Review 11th Edition

by pranavc » Mon Jun 02, 2008 5:52 pm
Hi All,
I got this question wrong and am far from convinced with the explanation for the answer. The question is as follows:

On a recent trip, Cindy drove her car 290 miles, rounded to the nearest 10 miles, and used 12 gallons of gasoline, rounded to the nearest gallon. The actual number of miles per gallon that Cindy's car got on this trip must have been between

(A) 290/12.5 and 290/11.4

(B) 295/12 and 284/11.4

(C) 284/12 and 295/12

(D) 284/12.5 and 295/11.4

(E) 295/12.5 and 284/11.4

Any input would be much appreciated. Thanks in advance.

Regards,

Pranav
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by chidcguy » Mon Jun 02, 2008 8:17 pm
290 miles, rounded to the nearest 10 miles means 285-294

12 gallons of gasoline rounded to the nearest gallon means 11.5-12.4

actual number of miles per gallon that Cindy's car got on this trip must have been between is asking for the range ie lowest and highest possible mileage which is 285/12.4 and 294/11.5

That answer is clearly not in any of the 5 choices. It comes down to D & E which fiddle with these numbers and E definitely is not the one.

Why D is correct? possibly because no other answer is close.

284/12.5 and 295/11.4



The answer depends on what happens when numerator decreases and denominator increases and vice versa. It will decrease and increase.



285/12.4 (22.98) and 294/11.5 (25.56) is the exact range

284/12.5 (22.90) and 295/11.4 (25.87) is the answer

Guru's

Isn't the highest value as per answer D out of bounds the max value? I mean the max she should have gotten is 25.56 but D says 25.87? needless to say I used the calculator.

Oh wait a sec! I was comparing the other way around. The original answer range still lies with in the given answer range.

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by pranavc » Tue Jun 03, 2008 6:11 pm
OK. I think I am going to appear pretty dumb now. I interpreted 290 miles to the nearest 10 miles to be numbers like 290,380, 300 etc. Why does it translate to 285-294? Any input would be appreciated. Thanks in advance.

Regards,

Pranav
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by athinabean » Tue Jun 03, 2008 8:54 pm
basics! :)
285 rounded to the nearest 10 is 290 (the 5 in the units place kicks it up to the next number). Same with 294 - the 4 in the units place kicks it down to 290. 1, 2, 3, and 4 will kick it down; 5, 6, 7, 8, and 9 will push it up. Just like when you round up 1.6 it becomes 2.

I hope this makes sense....
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by niraj_a » Wed Jun 04, 2008 9:24 am
i was able to narrow it down to D and E pretty quick but picked E thinking that higher mileage travelled requires a larger amount of gas.

is there a way i could have picked D without figuring out the actual MPGs like chidcguy? what's the reasoning?
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by pranavc » Wed Jun 04, 2008 1:49 pm
athinabean wrote:basics! :)
285 rounded to the nearest 10 is 290 (the 5 in the units place kicks it up to the next number). Same with 294 - the 4 in the units place kicks it down to 290. 1, 2, 3, and 4 will kick it down; 5, 6, 7, 8, and 9 will push it up. Just like when you round up 1.6 it becomes 2.

I hope this makes sense....
Totally makes sense. This is my though process too - except I would have expected one of the two ends of the spectrum to be in at least one of the answer choices. When I did not see that, it left me stumped.
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