Is my set up right? A tank can be filled by pipe A in 3 hours and by pipe B in 5 hours. When the tank is full, it can be drained by pipe C in 4 hours. if the tank is initially empty and all three pipes are open, how many hours will it take to fill up the tank? Pipe A = 1/3 Pipe B = 1/5 Pipe C = 1/4 Let 1/h = length of time it will all three pipes to fill the tank. 1/3 + 1/5 + + 1/4 = 1/h You say?