Originally Posted by
apricissimus
Anyway, the point is that air resistance complicates things, but it's not the reason why the average mph in the problem in the OP isn't simply the average of the uphill speed and the downhill speed.
Yeah, the point of the assignment wasn't to explore the affects of power, wind resistance, etc. on how fast you can go. It was to point out what I had thought was obvious: Its not the distance at a speed that influences MPH, its the time. After all, the H in MPH stands for "Hour". If we were discussing PPM (pace per mile), it would be different.