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    Question

    A cistern has two pipes one can fill it with water in 24

    hours and other can empty it in 9 hours. In how many hours will the cistern be emptied if both the pipes are opened together when (5 )/8th of the cistern is already filled with water?
    A 20 hours Correct Answer Incorrect Answer
    B 18 hours Correct Answer Incorrect Answer
    C 15 hours Correct Answer Incorrect Answer
    D 9 hours Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    If both pipes are open, then total units per hour empty the tank (A-B) = 3 - 8 = -5 units According to question, Tank has 5/8 of its total capacity in the beginning = 5/8 × 72 = 45 units Time taken to empty the tank = `45/(-5)` = 9 hours

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