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    Question

    Time taken by ‘A’ to fill a tank, which is 40%

    empty, is 20 minutes, while time taken by ‘B’ to fill the same tank, when it is 25% full, is 30 minutes. On a particular day, when the tank is completely empty, both pipes are opened together. Find the time (in minutes) after which ‘A’ must be closed so that the tank gets completely filled in 28 minutes.
    A 8 minutes Correct Answer Incorrect Answer
    B 10 minutes Correct Answer Incorrect Answer
    C 12 minutes Correct Answer Incorrect Answer
    D 15 minutes Correct Answer Incorrect Answer
    E 18 minutes Correct Answer Incorrect Answer

    Solution

    Time taken by ‘A’ to fill the empty tank = {20/0.4} = 50 minutes Time taken by ‘B’ to fill the empty tank = {30/0.75} = 40 minutes Let the total capacity of the tank be 200 litres Efficiency of ‘A’ = {200/50} = 4 litres/minute Efficiency of ‘B’ = {200/40} = 5 litres/minute Let the time after which ‘A’ is closed be T minutes. ATQ, (4 + 5)T + 5(28 - T) = 200 9T + 140 - 5T = 200 4T = 60 T = 15

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