Three pipes P Q and R can fill a Cistern in 6 hours After working at it together for 2 hours R is cl...........

Quantitative Aptitude ( CCS) Pipes&cistern

Three pipes P, Q and R can fill a Cistern in 6 hours. After working at it 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 to fill the Cistern is ?

14 hours

12 hours

15 hours

18 hours

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Explanation:

Answer & Explanation
Answer – A. 14 hours
Explanation :
Part filled in 2 hours = 2/6 = 1/3
Remaining Part = (1-1/3) = 2/3
(P + Q)’s 7 hour work = 2/3
(P + Q)’s 1 hour work = 2/21
R’s 1 hour work = (P + Q + R) 1 hour work – (P + Q) 1 hour work
= (1/6 – 2/21) = 1/14 = 14 hours