Word Problem

Question

A boat traveled 210 miles downstream and back. The trip downstream took 10 hours. The trip back took 70 hours. What is the speed of the boat in still water? What is the speed of the current?

Answer 1

210 round trip means 105 one way

d=rt

distance = rate of speed times time

t = d/r

10=105/(r+c) 70=105/(r-c)

10r + 10c = 105

70r-70c = 105

70r+70c =7(105)

140r = 8(105) = 840

r = 840/140 = 84/14 = 42/7 = 6 mph in still water

10c =105-60 = 45

c =45/10 = 4.5 mph = current speed