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 Post subject: GMAT Rate
PostPosted: Tue Feb 22, 2011 3:25 pm 
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A certain car can currently travel 17 miles per gallon of gasoline. After a tune-up, the car will use 80 percent as much gasoline as it does now. How many miles will the car be able to travel per gallon of gasoline after the tune-up?

A. 13.6
B. 15
C. 20.4
D. 21.25
E. 23.5

(D) After the tune-up, the car will travel 17 miles on 80% of a gallon of gasoline, which means it will travel 17 miles on 8/10, or 4/5, of a gallon of gasoline.

To solve for the number of miles that the car will be able to travel per one gallon of gasoline, we need to set up the following proportion:
17 miles is to 4/5 gallon as X miles is to 1 gallon.

Algebraically, this is expressed as:
17/(4/5) = X/1
X = 17 × 5/4
X = 85/4 = 21 1/4.

So the car will be able to travel 21.25 miles per gallon of gasoline after the tune-up.
The correct answer is choice (D).
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In this question you state that the car will use 80% AS MUCH GASOLINE AS IT DOES NOW. According to my understanding this should be - what the car uses now plus 80% not 80% of the current usage. Am I right? Or could you please explain the wording of the question? Thank you.


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 Post subject: Re: GMAT Rate
PostPosted: Tue Feb 22, 2011 3:29 pm 
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"the car will use 80 percent as much gasoline as it does now" means:
The car will use 80% of what it uses now.

"the car will use 80 percent MORE gasoline THAN it does now" would mean:
The car will use 80% MORE on top of 100% THAT it uses now. (in other words "180% of what it uses now").


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 Post subject: Re: GMAT Rate
PostPosted: Mon Jul 11, 2011 3:48 pm 
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This question is quite confusing. When you say the car will use 80% as much gasoline as it does now, this should mean 80% more of its current use not 80% of its current use, shouldn't it?


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 Post subject: Re: GMAT Rate
PostPosted: Mon Jul 11, 2011 4:10 pm 
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 Post subject: Re: GMAT Rate
PostPosted: Thu Sep 22, 2011 11:58 am 
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But the simplest way to calculate this is 17/0.8 and the answer will be 21.25.


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 Post subject: Re: GMAT Rate
PostPosted: Thu Sep 22, 2011 12:14 pm 
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