SOLUTION: I am trying to answer this question, but cannot understand it fully. If I cycle at 4 mph uphill, and 12 mph downhill, what is the average speed?

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Question 938478: I am trying to answer this question, but cannot understand it fully. If I cycle at 4 mph uphill, and 12 mph downhill, what is the average speed?
Found 2 solutions by Fombitz, Alan3354:
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Distance=Rate*Time
Assume the distance is D.
D=R%2At
So uphill,
D=4t
t=D%2F4
and downhill,
D=12t
t=D%2F12
Average speed is total distance over total time.
You travel a total of 2D
and it took D%2F4%2BD%2F12 in time so,
S=%282D%29%2F%28D%2F4%2BD%2F12%29
S=%282D%29%2F%28%283%2F12%29D%2BD%2F12%29
S=%282D%29%2F%28%284%2F12%29D%29
S=%282D%29%2F%28D%2F3%29
S=6 mph

Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
I am trying to answer this question, but cannot understand it fully. If I cycle at 4 mph uphill, and 12 mph downhill, what is the average speed?
=============
Avg speed of a round trip = 2*4*12/(4+12) = 96/16
= 6 mi/hr