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    Question

    Pipe ‘A’ can fill a tank in 20 hours while pipe

    ‘B’ takes 40 hours to empty it. Pipe ‘A’ is opened alone when the tank was empty and after 10 hours pipe ‘B’ is also opened. In how much time will the tank get filled completely?
    A 35 hours Correct Answer Incorrect Answer
    B 33 hours Correct Answer Incorrect Answer
    C 30 hours Correct Answer Incorrect Answer
    D 37 hours Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the total capacity of the tank be 40 units Efficiency of pipe ‘A’ = 40/20 = 2 units/hour Efficiency of pipe ‘B’ = 40/40 = 1 units/hour Tank filled in 10 hours = 10 × 2 = 20 units Therefore, required time taken to fill the remaining tank = (40 – 20)/(2 – 1) = 20 hours Therefore, total time taken = 10 + 20 = 30 hours

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