A car traveled 462 miles per tankful of gasoline on the high

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BTGmoderatorDC: Moderator; Posts: 7187; Joined: Thu Sep 07, 2017 4:43 pm; Followed by:23 members

A car traveled 462 miles per tankful of gasoline on the high

by BTGmoderatorDC » Mon Dec 16, 2019 7:15 pm

A car traveled 462 miles per tankful of gasoline on the highway and 336 miles per tankful of gasoline in the city. If the car traveled 6 fewer miles per gallon in the city than on the highway, how many miles per gallon did the car travel in the city?

(A) 14
(B) 16
(C) 21
(D) 22
(E) 27

OA B

Source: Official Guide

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Source: Beat The GMAT — Problem Solving | Mon Dec 16, 2019 7:15 pm

Gene@KaplanGMAT: Junior | Next Rank: 30 Posts; Posts: 15; Joined: Tue Dec 03, 2019 7:29 am

by Gene@KaplanGMAT » Tue Dec 17, 2019 5:32 pm

If a tank has x gallons, then....

On the highway you're getting 462/x mpg
In the city you're getting 336/x mpg

With 6 fewer mpg in the city, then 462/x - 336/x = 6 Multiply both sides by x.....
462 - 336 = 6x
126 = 6x
21 = x That's in the answer choices as (C), as a TRAP.

Your city mpg is 336/x, so that's 336/21 = 16. Answer choice (B).

I would also add this would be a good Backsolving problem. And if you're running out of time and have to make a strategic guess, figure there will probably be some trap answer that represents HIGHWAY mpg's, so odds are the right answer will be 6 smaller than another answer choice. The only answers here that fit that description are (B) (which is 6 smaller than D), and (C) (which is 6 smaller than E).

Gene Suhir
GMAT Score: 750
GMAT/GRE/LSAT Live Online Teacher
Kaplan Test Prep and Admissions
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Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Sat Dec 21, 2019 7:19 pm

BTGmoderatorDC wrote:A car traveled 462 miles per tankful of gasoline on the highway and 336 miles per tankful of gasoline in the city. If the car traveled 6 fewer miles per gallon in the city than on the highway, how many miles per gallon did the car travel in the city?

(A) 14
(B) 16
(C) 21
(D) 22
(E) 27

OA B

Source: Official Guide

We can create the proportion in which x = miles per gallon on the highway and (x - 6) = miles per gallon in the city.

(x - 6)/336 = x/462

462x - 2,772 = 336x

126x = 2,772

x = 22

So city mpg = 22 - 6 = 16 mpg.

Alternate Solution:

Let the capacity of the car be n gallons. Then, the car's gas mileage is 462/n miles per gallon on the highway and 336/n miles per gallon in the city. Since we are given that the difference is 6, we have:

462/n - 336/n = 6

126 = 6n

n = 21

Since the capacity of the car is 21 gallons, the car made 336/21 = 16 miles per gallon in the city.

Answer: B

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GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Sat Dec 21, 2019 7:19 pm

BTGmoderatorDC wrote:A car traveled 462 miles per tankful of gasoline on the highway and 336 miles per tankful of gasoline in the city. If the car traveled 6 fewer miles per gallon in the city than on the highway, how many miles per gallon did the car travel in the city?

(A) 14
(B) 16
(C) 21
(D) 22
(E) 27

OA B

Source: Official Guide