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    Question

    Time taken by β€˜A’ to fill a tank, which is 60%

    empty, is 24 minutes, while time taken by β€˜B’ to fill the same tank, when it is 40% full, is 30 minutes. When the tank is completely empty, both pipes are opened together. Find the time after which β€˜A’ must be closed so that the tank gets filled in 28 minutes.
    A 12 minutes 30 seconds Correct Answer Incorrect Answer
    B 14 minutes 24 seconds Correct Answer Incorrect Answer
    C 17 minutes 36 seconds Correct Answer Incorrect Answer
    D 18 minutes 12 seconds Correct Answer Incorrect Answer
    E 20 minutes 20 seconds Correct Answer Incorrect Answer

    Solution

    Time taken by β€˜A’ to fill the empty tank = {24/0.6} = 40 minutes Time taken by β€˜B’ to fill the empty tank = {30/0.6} = 50 minutes Let the total capacity of the tank be 200 litres Efficiency of β€˜A’ = {200/40} = 5 litres/minute Efficiency of β€˜B’ = {200/50} = 4 litres/minute Let the time after which β€˜A’ is closed be T minutes. ATQ, (5 + 4)T + 4(28 - T) = 200 9T + 112 - 4T = 200 5T = 88 T = 17.6 or 17 minutes 36 seconds

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