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      Question

      Time taken by β€˜A’ to fill a tank, which is 40%

      empty, is 20 minutes, while time taken by β€˜B’ to fill the same tank, when it is 25% full, is 30 minutes. On a particular day, when the tank is completely empty, both pipes are opened together. Find the time (in minutes) after which β€˜A’ must be closed so that the tank gets completely filled in 28 minutes.
      A 8 minutes Correct Answer Incorrect Answer
      B 10 minutes Correct Answer Incorrect Answer
      C 12 minutes Correct Answer Incorrect Answer
      D 15 minutes Correct Answer Incorrect Answer
      E 18 minutes Correct Answer Incorrect Answer

      Solution

      Time taken by β€˜A’ to fill the empty tank = {20/0.4} = 50 minutes Time taken by β€˜B’ to fill the empty tank = {30/0.75} = 40 minutes Let the total capacity of the tank be 200 litres Efficiency of β€˜A’ = {200/50} = 4 litres/minute Efficiency of β€˜B’ = {200/40} = 5 litres/minute Let the time after which β€˜A’ is closed be T minutes. ATQ, (4 + 5)T + 5(28 - T) = 200 9T + 140 - 5T = 200 4T = 60 T = 15

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