Two pipes P and Q can fill the tank alone in 60 and 90 hours respectively. If they are opened together, then in how many hours will the tank be filled?

Two pipes P and Q can fill the tank alone in 60 and 90 hours respectiv

1.	Two pipes P and Q can fill the tank alone in 60 and 90 hours respectively. If they are opened together, then in how many hours will the tank be filled?
A.	35
B.	32
C.	36
D.	30
Answer» D. 30