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Work/Rate Problems

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by swerve » Fri Feb 21, 2020 4:33 pm

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Answers

A

B

C

D

E

Stats

Difficulty—

A certain car uses one gallon of gasoline every 30 miles when it travels on the highway, and one gallon of gasoline every 20 miles when it travels in the city. When a car travels 4 miles on the highway and 4 additional miles in the city, it uses what percent more gasoline than if it travels 8 miles on the highway?

A. 15%
B. 20%
C. 22.5%
D. 25%
E. 50%

The OA is D

Source: Economist GMAT
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Re: Work/Rate Problems

by deloitte247 » Thu Feb 27, 2020 10:29 pm
On the highway, the car use 1 gallon per 36 miles
In the city, it uses 1 gallon per 20 miles
No. of gallons used to travel 4 miles on the highway = 4/30 = 0.133
No. of gallons used to travel 4 miles in the city = 4/20 = 0.2
No. of gallons used to travel 8 miles on the highway = 8/30 = 0.267
The % difference from gallons used to travel 8 miles on the highway =
$$\frac{0.333-0.267}{0.267}\cdot\frac{100}{1}$$
$$=\frac{0.066}{0.267}\cdot\frac{100}{1}$$
$$=24.7\approx25\%$$
Answer = option D
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Re: Work/Rate Problems

by Scott@TargetTestPrep » Sun Mar 01, 2020 1:10 pm
swerve wrote: ↑
Fri Feb 21, 2020 4:33 pm
 A certain car uses one gallon of gasoline every 30 miles when it travels on the highway, and one gallon of gasoline every 20 miles when it travels in the city. When a car travels 4 miles on the highway and 4 additional miles in the city, it uses what percent more gasoline than if it travels 8 miles on the highway?

A. 15%
B. 20%
C. 22.5%
D. 25%
E. 50%

The OA is D

Source: Economist GMAT
When the car travels 4 miles on the highway and another 4 miles in the city, it needs 4/30 + 4/20 = 8/60 + 12/60 = 20/60 = 1/3 gallon of gasoline.

When the car travels 8 miles on the highway, it needs 8/30 = 4/15 gallons of gasoline.

Therefore, the former option is:

(1/3 - 4/15) / (4/15) x 100 = (5 - 4) / 4 x 100 = 1/4 x 100 = 25 percent more than the latter.

Answer: D

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