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certain car averages 25 miles per gallon

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ambikasrinivas
 Post subject: certain car averages 25 miles per gallon
 Post Posted: Sun Jun 05, 2011 8:26 pm 
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Course Students


Posts: 13
From GMAT Prep Exam

A certain car averages 25 miles per gallon of gasoline when driven in the city, and 40 miles per gallon when driven on the highway. According to these rates, which of the following is closest to the number of miles per gallon that the car averages when it is driven 10 miles in the city and then 50 miles on the highway?

a. 28
b. 30
c. 33
d. 36
e. 38

Correct answer is 36. When I solved this, I got 37.5, so I rounded up to 38. I did 25x10 + 40x50 = 2250/60 = 37.5.

What did I do wrong?
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george.kourdin
 Post subject: Re: certain car averages 25 miles per gallon
 Post Posted: Mon Jun 06, 2011 12:00 am 
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Posts: 98
thats probably what they want us to do

cant avg distance. need to do time - i.e. time spending driving at each speed/total distance traveled
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ambikasrinivas
 Post subject: Re: certain car averages 25 miles per gallon
 Post Posted: Mon Jun 06, 2011 1:17 am 
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Posts: 13
not sure I follow you.

my answer (37.5) is wrong because it rounds up to 38...the correct answer is 36
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varun_783
 Post subject: Re: certain car averages 25 miles per gallon
 Post Posted: Mon Jun 06, 2011 2:12 am 
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Course Students


Posts: 263
Hi,

This is how I would solve the question:

Number of gallons used for the 10 miles in the city: 10/25 = 0.40

Number of gallons used for the 50 miles on the highway: 50/40 = 1.25

Total = 0.40 + 1.25 = 1.65 gallons

Average miles/gallon = Total distance traveled/Total gallons used

=> 60/1.65 = 36.3 or approx 36 miles/gallon

Hope that makes sense

Regards

Sunil
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ambikasrinivas
 Post subject: Re: certain car averages 25 miles per gallon
 Post Posted: Mon Jun 06, 2011 6:04 pm 
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Posts: 13
thanks!
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RonPurewal
 Post subject: Re: certain car averages 25 miles per gallon
 Post Posted: Tue Jun 07, 2011 8:07 am 
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ManhattanGMAT Staff


Posts: 7146
PEOPLE!
SEARCH THE FORUMS, please. wouldn't you rather just see the answer to your question than have to wait for it?

look here
post11873.html#p11873
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