Edward 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 6 miles per hour and returns along the same route at an average speed of 9 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:	A) 5.5	B) 5.8	C) 6.0	D) 6.3	E) 7.2
to calculate average of 2 speeds a and b when distance is constant   Formula - 2ab/(a+b)   Here 7.2dward's uphill speed = 6 mph   7.2dward's downhill speed = 9 mph   2*6*9/(6+9) = 108/15= 
<gadget id="calculator">108/15</gadget>
<output>36/5 = around 7.2</output>
7.2   Correct answer - 7.2
<result>E</result>
Edward 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 6 miles per hour and returns along the same route at an average speed of 9 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?