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    Question

    Pipes P and Q can fill a tank in 12 hours and 15 hours

    respectively, while a third pipe C can empty the tank in 24 hours. If all three pipes are opened simultaneously at 4:00 a.m., at what time will the tank be 65% full?
    A 10 am Correct Answer Incorrect Answer
    B 9 am Correct Answer Incorrect Answer
    C 9.15 am Correct Answer Incorrect Answer
    D 10.25 am Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the capacity of the tank be 120 units

    Efficiency of pipe ‘A’ = 120/12 = 10 units/hour

    Efficiency of pipe ‘B’ = 120/15 = 8 units/hour

    Efficiency of pipe ‘C’ = 120/24 = 5 units/hour

    Tank filled in 1 hour = 10 + 8 – 5 = 13 units

    Time taken to fill 65% of the tank = 0.65 × 120/13 = 6 hours

    Therefore, tank will get filled at (4 + 6) = 10 a.m.

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