the current in a river is 10 mph . a boat can travel 50 mph in still water . how far up the river can the boat travel if the round trip is to take 5 hours ?
upstream speed = 50 - 10 = 40 mph downstream speed = 50 + 10 = 60 mph d / 40 + d / 60 = 5 hours solving for d we get d = 120 answer : a
divide(multiply(multiply(subtract(50, 10), add(50, 10)), 5), add(add(50, 10), subtract(50, 10)))