Three pipes P, Q and R, together take four hours to fill a tank. All the three pipes were opened at the same time. After three hours, P was closed, and Q and R filled the remaining tank in two hours. How many hours will P alone take to fill the tank?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 8.
Let the total work to be done is 4 units.
Part of work done in 3 hours = 3/4
Remaining part = 1 - 3/4
⇒ 1/4
(Q + R)'s 1 hour work = 1/4 × 1/2
⇒ 1/8
P's 1 hour work = (P + Q + R)'q 1 hour work - (Q + R)'s 1 hour work
⇒ 1/4 - 1/8 = 1/8
P can complete the total work in 8 hours.