Juan goes out cycling outdoors. He travels at an average speed of 15 km/h...

[BTGmoderatorLU]

Source: Economist GMAT

Juan goes out cycling outdoors. He travels at an average speed of 15 km/h, to the top of the hill where the midpoint of the trip is. Going down hill, Juan travels at an average speed of 20 km/h. Which of the following is the closest approximation of Juan's average speed, in kilometers per hour, for the round trip?

A. 15.0
B. 17.1
C. 17.5
D. 17.9
E. 20.0

The OA is B

[Scott@TargetTestPrep]

Source: Economist GMAT

Juan goes out cycling outdoors. He travels at an average speed of 15 km/h, to the top of the hill where the midpoint of the trip is. Going down hill, Juan travels at an average speed of 20 km/h. Which of the following is the closest approximation of Juan's average speed, in kilometers per hour, for the round trip?

A. 15.0
B. 17.1
C. 17.5
D. 17.9
E. 20.0

The OA is B

We can let the one-way trip be 60 miles; therefore, we have:

Average Speed = (Total Distance)/(Total Time)

Average Speed = (60 + 60)/(60/15 + 60/20)

Average Speed = 120/7

Average Speed ≈ 17.1

Answer: B