Problem: the current in a river is 5 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 ?
Rationale: "upstream speed = 20 - 5 = 15 mph downstream speed = 20 + 5 = 25 mph d / 15 + d / 25 = 10 hours solving for d we get d = 93,75 answer : c"
annotated_formula: divide(multiply(multiply(subtract(20, 5), add(20, 5)), 10), add(add(20, 5), subtract(20, 5)))