GmatKiss wrote:On Valentine's Day, a busy florist drove his delivery truck from Palm Beach to Miami at an average rate of 45 miles per hour. On his return trip to Palm Beach, he encountered rush hour traffic, which slowed him to an average speed of 25 miles per hour. What was the driver's average speed for the trip, in miles per hour?
a. 30
b. 32
c. 35
d. 36
e. 38
The average speed here is not an integer value.
The question really should ask for the APPROXIMATE average speed.
The ratio of the TIMES there and back is the RECIPROCAL of the ratio of the RATES there and back.
Since the ratio of the rates there and back = 45:25 = 9:5, the ratio of the times there and back = 5:9.
Thus, of every 14 hours traveled, 5 hours will be at 45mph and 9 hours will be at 25mph.
Thus, the average speed for the whole trip = (5*45 + 9*25)/14 ≃ (225+225)/14 ≃ 32.
The correct answer is
B.
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