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    Question

    Pipe ‘A’ can fill 25% of a tank in 4 hours

    while pipe ‘B’ takes 20 hours to empty fully filled tank. Pipe ‘A’ is opened alone when the tank was empty. After 14 hours, pipe ‘B’ is also opened. In how much time the tank will get filled this way?
    A 34 hours Correct Answer Incorrect Answer
    B 30 hours Correct Answer Incorrect Answer
    C 24 hours Correct Answer Incorrect Answer
    D 28 hours Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Time taken by pipe ‘A’ to fill the tank = 4/0.25 = 16 hours
    Let, the total capacity of the tank be 80 units
    Efficiency of pipe ‘A’ = 80/16 = 5 units/hour
    Efficiency of pipe ‘B’ = 80/20 = 4 units/hour
    Tank filled in 14 hours = 5 × 14 = 70 units
    Time taken by pipe ‘A’ and pipe ‘B’ to fill the remaining tank = (80 – 70)/(5 – 4) = 10 hours
    Therefore, total time taken = 10 + 14 = 24 hours

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