two pipes a and b can separately fill a tank in 12 and 20 minutes respectively . a third pipe c can drain off 45 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 ?
1 / 12 + 1 / 20 - 1 / x = 1 / 15 x = 15 15 * 45 = 675 answer : c
multiply(multiply(inverse(subtract(add(add(divide(const_1, 12), divide(const_1, 20)), divide(const_1, 45)), divide(const_1, 15))), const_3), 20)