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      Question

      Pipes X and Y alone can fill a tank in 8 hours and 3 hours

      respectively. When both pipes along with pipe Z, an outlet pipe, are opened together, 5/12 of the tank gets filled in 60 minutes. Find the time taken by pipe Z to empty a completely filled tank.
      A 12 hours Correct Answer Incorrect Answer
      B 18 hours Correct Answer Incorrect Answer
      C 20 hours Correct Answer Incorrect Answer
      D 24 hours Correct Answer Incorrect Answer
      E 30 hours Correct Answer Incorrect Answer

      Solution

      Let the total capacity of the tank be 24 litres.
      Efficiency of Pipe 'X' = 24 / 8 = 3 litres/hour
      Efficiency of Pipe 'Y' = 24 / 3 = 8 litres/hour
      Let pipe 'Z' empties the tank with an efficiency of 'm' litres/hour.
      Tank filled in 60 minutes = (5/12) Γ— 24 = 10 litres
      ATQ,
      (3 + 8 - m) Γ— (60/60) = 10
      (11 - m) Γ— 1 = 10
      11 - m = 10
      m = 1 litres/hour
      Time taken by Z to empty the tank = 24 / 1 = 24 hours

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