BD Merit - Freelancing, BCS, Bank, Primary, Admission, NTRCA

1 . Three pipes P,Q and R can fill a tank in 6 hours. After working all three together for 2 hours. R is closed and P and Q can fill the remaining part in 7 hours . The number of hours taken by R alone fill the thank is --

A. 10
B. 12
C. 14
D. 16
D. None

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Answer: Option C

Explanation:

P, Q & R alltogether can fill 1/6 th of the tank in 1 hour

So, in 2 hours they fill = 2×1/6 = 1/3 of the tank

Remining part to be filled = 1 - 1/3 = 2/3 of the tank

P & Q together in 7 hours can fill 2/3 of the tank

So, P & Q together in hour can fill = 2/(3×7) = 2/21 of the tank

So, R alone can fill in 1 hour = 1/6 - 2/21 = (7 - 4)/42 = 1/14 of the tank

Therefore, R alone can fill the tank in 14 hours.

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