GMATPrep 1 Rate Problem

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GMATPrep 1 Rate Problem

by Mjkourtis » Sat Oct 13, 2012 9:41 am
At a speed of 50 mph, a car used 1 gallon every 30 miles. If the car starts with a full tank of 12 gallons and travels for 5 hours at 50 mpg, the amount of gas used would be what fraction of full tank?

A. 3/25
B. 11/36
C. 7/12
D. 2/3
E. 25/36

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by GMATGuruNY » Sat Oct 13, 2012 2:07 pm
Mjkourtis wrote:At a speed of 50 mph, a car used 1 gallon every 30 miles. If the car starts with a full tank of 12 gallons and travels for 5 hours at 50 mpg, the amount of gas used would be what fraction of full tank?

A. 3/25
B. 11/36
C. 7/12
D. 2/3
E. 25/36
Distance traveled = r*t = 50*5 = 250 miles.

To determine the amount of gas used in 250 miles, set up a proportion:
1 gallon/30 miles = x gallons/250 miles
x = 250/30 = 25/3 gallons.

Gas used/tank = (25/3)/12 = 25/36.

The correct answer is E.
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by Anurag@Gurome » Sat Oct 13, 2012 9:38 pm
Mjkourtis wrote:At a speed of 50 mph, a car used 1 gallon every 30 miles. If the car starts with a full tank of 12 gallons and travels for 5 hours at 50 mpg, the amount of gas used would be what fraction of full tank?

A. 3/25
B. 11/36
C. 7/12
D. 2/3
E. 25/36
Total distance 50 * 5 = 250 miles
Gas consumed = 250/30 = 25/3 gallons

Fraction of gas = (25/3)/12 = [spoiler]25/36[/spoiler]

The correct answer is E.
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