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      Question

      Pipe ‘A’ takes 20 hours to fill a tank. Pipe ‘B’

      takes 80 hours to empty the same tank. If both are opened together, then how long will it take to fill 75% of the tank?
      A 20 hours Correct Answer Incorrect Answer
      B 18 hours Correct Answer Incorrect Answer
      C 19 hours Correct Answer Incorrect Answer
      D 21 hours Correct Answer Incorrect Answer

      Solution

      Let the capacity of the tank be 160 litres.So, efficiency of pipe ‘A’ = 160 ÷ A = 8 litres/hour And efficiency of pipe ‘B’ = 160 ÷ B = 2 litres/hour So, combined efficiency of both pipes = 8 – 2 = 6 litres/hour So, time taken to fill 75% of the tank = (160 × 0.75) ÷ 6 = 120 ÷ 6 = 20 hours

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