A motorboat covers the distance from one pier to the other pier in 4 hours and the way back in 5 hours. What is the speed of the boat in still water, if it covers 70 km with the current in 3.5 hours?
(its not 20 i tried)
r = speed in still water r + c = speed with current r - c = speed against current
3.5(r + c) = 70 r + c = 20 c = 20 - r
4(r + c) = distance from pier to pier 5(r - c) = distance from pier to pier 4(r + c) = 5(r - c) 4(r + 20 - r) = 5(r - 20 + r) 80 = 10r - 100 180 = 10r 18 = r The speed in still water is 18 km/hour
