the current in a river is 6 mph . a boat can travel 20 mph in still water . how far up the river can the boat travel if the round trip is to take 10 hours ?
"upstream speed = 20 - 6 = 14 mph downstream speed = 20 + 6 = 26 mph d / 14 + d / 26 = 10 hours solving for d we get d = 91 answer : d"
divide(multiply(multiply(subtract(20, 6), add(20, 6)), 10), add(add(20, 6), subtract(20, 6)))