A cistern can be filled in 6 hours by taps P and  If tap R also joins them, then cistern is filled in 5 hours. Tap P can fill the cistern at twice the rate of tap  In what time tap Q and R fill the cistern?
A.9.75 hours
B.10. 90 hours
C.11.25 hours
D.12.90 hours
Answer:C
A cistern can be filled in 6 hours by taps P and  If tap R also joins them, then cistern is filled in 5 hours. Tap P can fill the cistern at twice the rate of tap  In what time tap Q and R fill the cistern?
A.9.75 hours B.10. 90 hours C.11.25 hours D.12.90 hours