Question

    Pipes ‘M’ and ‘N’ alone can fill a tank in 14

    minutes and 21 minutes, respectively, while pipe ‘O’ can empty the same tank in 42 minutes. If all three pipes are opened together, then find the time taken to fill the tank.
    A 4 mins Correct Answer Incorrect Answer
    B 9 mins Correct Answer Incorrect Answer
    C 12 mins Correct Answer Incorrect Answer
    D 10 mins Correct Answer Incorrect Answer

    Solution

    ATQ,
    Let the capacity of the tank be 84 litres {LCM (14, 21, and 42)}
    Efficiency of pipe ‘M’ = (84/14) = 6 litres/minute
    Efficiency of pipe ‘N’ = (84/21) = 4 litres/minute
    Efficiency of pipe ‘O’ = (84/42) = 2 litres/minute
    Required time = {84 / (6 + 4 – 2)} = 12 minutes

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