Discussion of Question with ID = 021 under Pipes-and-Cisterns

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Pipe A can fill a cistern in 30 minutes, while the pipe B can fill it in 20 minutes. They are alternately open for 1 minute. How long will it take the cistern to fill completely?


24 mins.


25 mins.


23 mins.


26 mins.

Ans: a

Let the total time taken be 2x minutes. Both X and Y run for x mins. So $(x/20 + x/30)$ = 1. Solving for x, we get x = 12, which gives 2x = 24.

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