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    Question

    Pipe ‘A’ takes 40 minutes to fill a tank.

    Pipe ‘B’ takes 50 minutes to empty the same tank. If pipe ‘B’ is opened 21 minutes after pipe ‘A’, then find the total time taken to fill the tank in this manner.
    A 121 minutes Correct Answer Incorrect Answer
    B 103 minutes Correct Answer Incorrect Answer
    C 116 minutes Correct Answer Incorrect Answer
    D 60 minutes Correct Answer Incorrect Answer

    Solution

    Let the capacity of the tank be ‘200’ litres {LCM (40, 50)} Efficiency of pipe ‘A’ = (200/40) = 5 litres/minute Efficiency of pipe ‘B’ = (200/50) = 4 litres/minute Quantity of water filled by pipe ‘A’ in 21 minutes = 5 × 21 = 105 litres Quantity of water to be filled = 200 – 105 = 95 litres Time taken by pipe ‘A’ and ‘B’ together to fill 95 litres of water = {95/(5 – 4)} = 95 minutes Total time taken = 21 + 95 = 116 minutes

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