Harry is a trail runner who decides to take a day off work to run up and down a local mountain. He runs uphill at an average speed of 5 miles per hour and returns along the same route at an average speed of 10 miles per hour. Of the following, which is the closest to his average speed, in miles per hour, for the trip up and down the mountain? Choose the correct choice from the following options:
A) 5.5
B) 5.8
C) 6.0
D) 6.3
E) 6.6
to calculate average of 2 speeds a and b when distance is constant   Formula - 2ab/(a+b)   Here Harry's uphill speed = 5 mph   Harry's downhill speed = 10 mph   2*5*10/(5+10) = 100/15 = 6.6   Correct answer - 6.6
<result>E</result>
Harry is a trail runner who decides to take a day off work to run up and down a local mountain. He runs uphill at an average speed of 5 miles per hour and returns along the same route at an average speed of 10 miles per hour. Of the following, which is the closest to his average speed, in miles per hour, for the trip up and down the mountain?