Question 9
A tank is connected with 3 pipes P, Q, R. Pipes P and Q are inlet pipes and pipe R is an outlet pipe. Pipe P and Q fill the tank in 6 hours and 5 hours respectively and R empties the tank in 3 hours. If pipe P is opened at 7 PM and Q is opened at 8 PM and R is opened at 9 PM. What time does the cistern get filled?