SSC Quantitative Aptitude Pipes & Cisterns Question Bank Pipe and Cistern (II)

A cistern can be filled by two pipes A and B in 20 min and 30 min, respectively. Both the pipes are opened together when the cistern is empty but after sometime, A is stopped and the cistern is filled in 18 min in all. The time (in min) after which A is stopped, is

A) 6

B) 8

C) 9

D) 12

Correct Answer: B

Solution :

[b] Let the time after which the pipe A was stopped be x min. Then,\[\frac{x}{20}+\frac{18}{30}=1\]\[\Rightarrow \]\[\frac{3x+36}{60}=1\] \[\Rightarrow \] \[3x=60-36\]\[\Rightarrow \]\[x=8\min \]

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