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      Question

      Two pipes A and B can fill a cistern in  27 (1/2) 

      minutes and 35 minutes respectively. Both pipes are opened. The cistern will be filled in just 25 minutes, if the pipe B is turned off after:
      A 5(1/11) minutes Correct Answer Incorrect Answer
      B 7(5/11) minutes Correct Answer Incorrect Answer
      C 3(2/11) minutes Correct Answer Incorrect Answer
      D 9(6/11) minutes Correct Answer Incorrect Answer

      Solution

      Let the pipe B be turned off after x  minutes Then, Part filled by (A + B) in x  minutes + Part filled by A in (25 - x)  minutes = 1 x(2/55 - 1/35) + (25 - x) x 2/55 = 1 x/35 = 1 - 50/55  x = 35/11   or  3(2/11) minutes 

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