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    Question

    Pipe ‘M’ and pipe ‘N’ together can fill an empty

    tank in 30 hours while pipe ‘N’ and pipe ‘O’ together take 20 hours to fill the same tank. If the efficiency of pipe ‘O’ is twice that of pipe ‘M’, then find the time taken by pipe ‘N’ to fill the tank alone.
    A 60 hrs Correct Answer Incorrect Answer
    B 36 hrs Correct Answer Incorrect Answer
    C 75 hrs Correct Answer Incorrect Answer
    D 45 hrs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ, Let the total capacity of the tank = 120 units Efficiency of pipes (M + N) = 120/30 = 4 units/hour Efficiency of pipes (N + O) = 120/20 = 6 units/hour Let the efficiency of pipe ‘M’ = x units/hour Therefore, efficiency of pipe ‘O’ = 2x units/hour Therefore, 2x – x = 6 – 4 Or, x = 2 Therefore, efficiency of pipe ‘N’ = 4 – 2 = 2 units/hour Time taken by pipe ‘N’ to fill the tank alone = 120/2 = 60 hours

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