Miles drives the same path to and from work. If he averages 50 miles per hour on the way to work and 75 miles per hour on the way from work, what is the average speed of his entire commute?
+129847 Avg speed =
2* product of speeds / sum of speeds =
(2 * 50 * 75) /( 50 + 75) =
7500 / 125 =
60 mph
[ NOT (50 + 75) / 2 = 125 / 2 = 62.5 mph as many think !!! ]
+37146 Time to work = distance / rate = d/50
Time from work = d/75
total distance = 2d
total distance / total time = average rate
2d / (d/50 + d/75) = 2 / ( 1/50 + 1/75) = 2 / (3/150 + 2/150) = 2/ (5/150) = 300/5 = 60 m/hr ( as Chris found via different method !)
