the current in a river is 8 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 - 8 = 12 mph downstream speed = 20 + 8 = 28 mph d / 12 + d / 28 = 10 hours solving for d we get d = 84 answer : b"
divide(multiply(multiply(subtract(20, 8), add(20, 8)), 10), add(add(20, 8), subtract(20, 8)))