A certain car averages 25 miles per gallon when driving

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VJesus12: Legendary Member; Posts: 2276; Joined: Sat Oct 14, 2017 6:10 am; Followed by:3 members

A certain car averages 25 miles per gallon when driving

by VJesus12 » Sat Apr 20, 2019 3:05 am

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A certain car averages 25 miles per gallon when driving in the city and 40 miles per gallon when driving 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

[spoiler]OA=D[/spoiler]

Source: GMAT Prep

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Source: Beat The GMAT — Problem Solving | Sat Apr 20, 2019 3:05 am

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Jay@ManhattanReview: GMAT Instructor; Posts: 3008; Joined: Mon Aug 22, 2016 6:19 am; Location: Grand Central / New York; Thanked: 470 times; Followed by:34 members

by Jay@ManhattanReview » Sun Apr 21, 2019 11:43 pm

VJesus12 wrote:A certain car averages 25 miles per gallon when driving in the city and 40 miles per gallon when driving 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

[spoiler]OA=D[/spoiler]

Source: GMAT Prep

Time taken to drive 10 miles in city = 10/25 = 2/5 hours;
Time taken to drive 50 miles in city = 50/40 = 5/4 hours

Total time taken = 2/5 + 5/4 = 33/20 hours

Total distance = 10 + 50 = 60 miles

Average speed = Total distance / Total time = 60 / (33/20) = appx 36 miles per hour

The correct answer: D

Hope this helps!

-Jay
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Scott@TargetTestPrep: GMAT Instructor; Posts: 8083; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Tue Apr 23, 2019 7:03 pm

VJesus12 wrote:A certain car averages 25 miles per gallon when driving in the city and 40 miles per gallon when driving 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

[spoiler]OA=D[/spoiler]

Source: GMAT Prep

We can use the formula:

average = total distance/total gallons

average = 60/(10/25 + 50/40)

average = 60/(2/5 + 5/4)

average = 60/(8/20 + 25/20)

average = 60/(33/20)

average = 1200/33 â‰ˆ 36

Answer: D

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