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    Question

    Pipe M can fill a tank in 10 hours, and pipe N can do

    the same in 30 hours. Pipe O can drain half the tank in 6 hours. If all pipes are opened at once, how much time will it take to completely fill the tank?
    A 22 hrs Correct Answer Incorrect Answer
    B 12 hrs Correct Answer Incorrect Answer
    C 20 hrs Correct Answer Incorrect Answer
    D 30 hrs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Time taken to empty the full tank by pipe O = 6 × 2 = 12 hours Parts of the tank filled in 1 hour if all the pipes are opened together = (1/10) + (1/30) – (1/12) = (6 + 2 – 5)/60 = 3/60 = 1/20 So, required time to fill the tank = 1 / (1/20) = 20 hours

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