Problem: two pipes a and b can separately fill a tank in 10 and 15 minutes respectively . a third pipe c can drain off 20 liters of water per minute . if all the pipes are opened , the tank can be filled in 15 minutes . what is the capacity of the tank ?
Rationale: "1 / 10 + 1 / 15 - 1 / x = 1 / 15 x = 10 10 * 20 = 200 answer : c"
annotated_formula: multiply(multiply(inverse(subtract(add(add(divide(const_1, 10), divide(const_1, 15)), divide(const_1, 20)), divide(const_1, 15))), const_3), 15)