Quote:
Originally Posted by mpg_numbers_guy
40 MPH uphill and 75 MPH downhill, if split evenly, is an average speed of 56.25 MPH, which is pretty much the same speed I averaged outside the mountains.

Not quite! There was a similar problem on my physics homework this week.
If you traveled the same time at each speed, your average speed would be the arithmetic mean of 40 and 75, or 57.5 mph. But since we're assuming an equal distance at each speedup the mountain and down the other sideyour average speed is the harmonic mean:
2/((1/40)+(1/75)) = 52.1739... mph
Of course, that's assuming instant acceleration for the sake of simplicity, which means that estimate is a little high.