Practice Test Discussion

Q)

Three pipes are fitted to a cistern. The empty cistern is filled by the first and the second taps in 3 and 4 h respectively. The full cistern is empties by the third tap in 5 h. If all the three taps are opened simultaneously, the empty cistern will be filled up in___ time.

[SSC Multitasking 2013]


  • Explanation

    According to the above given formula, If pipe A  and B fills a tank in x and y hours respectively, but a third pipe C empties the full tank in z hours then the net portion filled in 1 hour when all of them are opened together is xyzyz+xz-xy hours.

    So,

     3×4×5(4×5)+(3×5)-(3×4)=6023 or 21423hours

    Therefore, the tank will be filled in 21423 hours when all the pipes are opened simultaneously.

    Hence option B is correct.

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    Pipes and cisterns

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