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# A driver completed the first 20 miles of a 40-mile trip at an average

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Re: A driver completed the first 20 miles of a 40-mile trip at an average [#permalink]
Bunuel
A driver completed the first 20 miles of a 40-mile trip at an average speed of 50 miles per hour. At what average speed must the driver complete the remaining 20 miles to achieve an average speed of 60 miles per hour for the entire 40-mile trip? (Assume that the driver did not make any stops during the 40-mile trip.)

(A) 65 mph
(B) 68 mph
(C) 70 mph
(D) 75 mph
(E) 80 mph

We can use the average speed formula:
Average speed = Total Distance / Total Time (time for first 20 miles + time for last 20 miles)

60 = 40/ 20/50 + 20/x

60 = 40/ 20x/50x + 1000/50x

60 = 40 / 20x + 1000/50x

60 = 2000x / 20x + 1000

1200x + 60000 = 2000x
60000 = 800x
600/8 = x
75 = x

IMO Option D

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Re: A driver completed the first 20 miles of a 40-mile trip at an average [#permalink]
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