Bhanu Chaudhary
Poll
Professional
Asked: 2022-03-03T18:48:00+05:30

Two pipes P and Q can fill a cistern in 12 and 15 min, respectively. If both are opened together and at the end of 3 min, the first is closed. How much longer will the cistern take to fill?

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Two pipes P and Q can fill a cistern in 12 and 15 min, respectively. If both are opened together and at the end of 3 min, the first is closed. How much longer will the cistern take to fill?

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    1 Answer

    1. Professional

      Correct Answer: 8 1/4

      Part filled by pipe P in 1 min = 1/12

      Part filled by pipe Q in 1 min = 1/15

      Part filled by both pipes in 1 min

      = 1/12+ 1/15= 5+4/60= 9/60

      Now, part filled by both pipes in 3 min

      = 3×9/60=27/60=9/20

      Remaining part = 1−9/20=11/20

      Let the remaining part is filled by pipe Q in x min.

      Then, x×1/15=11/20

      x=15×11/20=3×11/4=33/4=8 1/4min

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