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    Question

    Pipe ‘A’ can fill a tank in 25 hours while pipe

    ‘B’ takes 30 hours to empty it. Pipe ‘A’ is opened alone when the tank was empty and after 12 hours pipe ‘B’ is also opened. In how much time will the tank get filled completely?
    A 90 hours Correct Answer Incorrect Answer
    B 20 hours Correct Answer Incorrect Answer
    C 80 hours Correct Answer Incorrect Answer
    D 60 hours Correct Answer Incorrect Answer

    Solution

    Let the total capacity of the tank be 150 units Efficiency of pipe ‘A’ = 150/25 = 6 units/hour Efficiency of pipe ‘B’ = 150/30 = 5 units/hour Tank filled in 12 hours = 12 × 6 = 72 units Therefore, required time taken to fill the remaining tank = (150 – 72)/(6 – 5) = 78 hours Therefore, total time taken = 12 + 78 = 90 hours

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