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    Question

    A cistern is normally filled in 18 hours, but it takes

    12 hours longer to fill because of a leak at its bottom. If the cistern is full, how long will it take to empty it?
    A 32 hrs Correct Answer Incorrect Answer
    B 36 hrs Correct Answer Incorrect Answer
    C 45 hrs Correct Answer Incorrect Answer
    D 52 hrs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let pipe is A and leak is B    A                          A+B    18                            30 Let total tank = LCM(18,30) = 90 L   5             :                   3 So 1 hr work of leak = 3 - 5 = -2 Therefore, the leak will drain all the water of the tank in 90/2 = 45 hours.

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