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    Question

    Pipe A can fill a tank in 10 hours, whereas pipe B can

    empty the same tank in 12 hours. If the two pipes are operated alternately for one hour each, starting with pipe A, how much time will it take to completely fill the tank?
    A 109 hrs Correct Answer Incorrect Answer
    B 112 hrs Correct Answer Incorrect Answer
    C 124 hrs Correct Answer Incorrect Answer
    D None of the above Correct Answer Incorrect Answer

    Solution

    Let the total capacity of the tank be 60 units

    Efficiency of pipe ‘A’ = 60/10 = 6 units/hour

    Efficiency of pipe ‘B’ = 60/12 = 5 units/hour

    Amount of tank filled in 2 hours = 6 – 5 = 1 units

    Therefore, amount of tank filled in (2 × 54) hours = 54 units

    Therefore, remaining six unit will be filled in 6/6 = 1 hour

    Total time taken = 2 × 54 + 1 = 109 hours

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