a cyclist bikes x distance at 8 miles per hour and returns over the same path at 10 miles per hour . what is the cyclist ' s average rate for the round trip in miles per hour ?
distance = d 1 = x miles speed = s 1 = 8 miles per hour time = t 1 = distance / speed = x / 8 2 . going from b to a distance = d 2 = x miles speed = s 2 = 10 miles per hour time = t 2 = distance / speed = x / 10 3 . average speed = total distance / total time total distance = x + x = 2 x total time = x / 10 + x / 8 = x ( 1 / 10 + 1 / 8 ) = = 9 x / 40 speed = 2 x / ( 9 x / 40 ) = 80 / 9 = 8.9 answer : b
divide(add(8, 10), const_2)