How to find average speed when distance not specified?

Science & Mathematics by Anonymous 2018-06-11 22:32:54

Social Science

2 answers

You drive to Point A at a brisk 50 mph. In the evening you return by the same route, but traffic has improved, so you go 75 mph. Not counting the time you spent , walking to your car, what was your average driving speed this blustery winter day?

Anonymous

Let distance to A = x miles t1 = x/50 hours t2 = x/75 hours Total time = x/50 + x/75 hours Time = 3x/150 + 2x/150 hours Time = 5x/150 = x/30 hours Average speed = 2x / [ x/30 ] = 60 mph
Anonymous

Harmonic mean applies 2(50*75)/(50+75) = 7500/125 = 60