Two inlet pipes A & B can fill an empty cistern in 12 hours & 36 hours respectively while Pipe C is an outlet pipe that can drain the filled cistern in 6 hours. When the cistern is full Pipe C is left open for an hour, then closed & Pipe A is opened for an hour, closed and Pipe B is opened for an hour. The process continues till the cistern is empty. How many hours will it take for the filled cistern to be emptied?

Two inlet pipes A & B can fill an empty cistern in 12 hours & 36 hours

1.	Two inlet pipes A & B can fill an empty cistern in 12 hours & 36 hours respectively while Pipe C is an outlet pipe that can drain the filled cistern in 6 hours. When the cistern is full Pipe C is left open for an hour, then closed & Pipe A is opened for an hour, closed and Pipe B is opened for an hour. The process continues till the cistern is empty. How many hours will it take for the filled cistern to be emptied?
A.	54
B.	46
C.	18
D.	52
Answer» C. 18