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Post subject: GMAT Rate Posted: Tue Feb 22, 2011 3:25 pm 

Joined: Sun May 30, 2010 3:15 am Posts: 424

A certain car can currently travel 17 miles per gallon of gasoline. After a tuneup, 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 tuneup?
A. 13.6 B. 15 C. 20.4 D. 21.25 E. 23.5
(D) After the tuneup, 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 tuneup. The correct answer is choice (D). 
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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Gennadiy

Post subject: Re: GMAT Rate Posted: Tue Feb 22, 2011 3:29 pm 

Joined: Sun May 30, 2010 2:23 am Posts: 498

"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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questioner

Post subject: Re: GMAT Rate Posted: Mon Jul 11, 2011 3:48 pm 

Joined: Sun May 30, 2010 3:15 am Posts: 424

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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Gennadiy

Post subject: Re: GMAT Rate Posted: Mon Jul 11, 2011 4:10 pm 

Joined: Sun May 30, 2010 2:23 am Posts: 498


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questioner

Post subject: Re: GMAT Rate Posted: Thu Sep 22, 2011 11:58 am 

Joined: Sun May 30, 2010 3:15 am Posts: 424

But the simplest way to calculate this is 17/0.8 and the answer will be 21.25.


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Gennadiy

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

Joined: Sun May 30, 2010 2:23 am Posts: 498


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