GMAT PREP Practice Test 2 PS

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GMAT PREP Practice Test 2 PS

by joonwons » Mon Jul 23, 2007 9:49 pm
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?

The answer is 36. Can somebody please help me out?

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by beny » Mon Jul 23, 2007 11:04 pm
Where the other answer choices really far from 36? The actual answer is 36 and change... but if it asks for the "closest" answer, and there is no answer closer to 36, I suppose 36 would suffice.

Here's how to do it:

The car averages 25 miles per gallon while in the city and it drives 10 miles in the city. Therefore, the total gas consumed in the city is 10/25 gallons.

The car averages 40 miles per gallon while on the highway and it drives 50 miles on the highway. Therefore, the total gas consumed on the highway is 50/40 gallons.

The total milage driven is 10 + 50 = 60 miles.
The total gas used is 10/25 + 50/40 = 33/20 gallons.

Approximate milage per gallon is calculated: 60/(33/20) = 1200/33 =~ 12/(1/3) = 36.
Last edited by beny on Tue Jul 24, 2007 5:57 pm, edited 1 time in total.

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by joonwons » Tue Jul 24, 2007 10:02 am
1. 28
2. 30
3. 33
4. 36 (Answer)
5. 38

Thank you so much for your help!