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    Question

    Pipe X can fill a tank in 72 minutes while pipe Y can

    fill the same tank in 90 minutes. If pipe X and Y are opened simultaneously, then after how much time must pipe X be closed so that the whole tank is filled in 54 minutes?
    A 144 min Correct Answer Incorrect Answer
    B 200 min Correct Answer Incorrect Answer
    C 90 min Correct Answer Incorrect Answer
    D 120 min Correct Answer Incorrect Answer

    Solution

    ATQ, Let the capacity of the tank = 360 liters (LCM of 72 and 90). Quantity of water filled by pipe X in one minute = 360 / 72 = 5 liters. Quantity of water filled by pipe Y in one minute = 360 / 90 = 4 liters. Let pipe X be closed after ‘x’ minutes. So, 5x + 4 × (54 – x) = 360 5x + 216 - 4x = 360 x = 144 x = 144/1 x = 144 So, pipe X must be closed after 144 minutes.

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