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      Question

      Pipe ‘A’ takes 30 minutes to fill a tank. Pipe

      ‘B’ takes 40 minutes to empty the same tank. If pipe ‘B’ is opened 20 minutes after pipe ‘A’, then find the total time taken to fill the tank in this manner.
      A 61 minutes Correct Answer Incorrect Answer
      B 63 minutes Correct Answer Incorrect Answer
      C 64 minutes Correct Answer Incorrect Answer
      D 60 minutes Correct Answer Incorrect Answer
      E 70 minutes Correct Answer Incorrect Answer

      Solution

      Let the capacity of the tank be ‘120’ litres {LCM (30, 40)} Efficiency of pipe ‘A’ = (120/30) = 4 litres/minute Efficiency of pipe ‘B’ = (120/40) = 3 litres/minute Quantity of water filled by pipe ‘A’ in 20 minutes = 4 × 20 = 80 litres Quantity of water to be filled = 120 – 80 = 40 litres Time taken by pipe ‘A’ and ‘B’ together to fill 40 litres of water = {40/(4 – 3)} = 40 minutes Total time taken = 20 + 40 = 60 minutes

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