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    Question

    Pipe ‘P’ alone can fill a tank in 12 minutes. If pipes

    ‘P’ and ‘Q’ are operated together, they fill the tank in 16 minutes. Find the time taken by pipe ‘Q’ alone to empty 75% of the tank.
    A 60 mins Correct Answer Incorrect Answer
    B 80 mins Correct Answer Incorrect Answer
    C 40 mins Correct Answer Incorrect Answer
    D 20 mins Correct Answer Incorrect Answer

    Solution

    ATQ,

    Let the total capacity of the container = L.C.M of 20 and 25 = 100 units

    So, efficiency of pipe 'X' alone = 100 ÷ 20 = 5 units/minute

    Combined efficiency of pipes 'X' and 'Y' = 100 ÷ 25 = 4 units/minute

    So, efficiency of pipe 'Y' alone = 4 - 5 = -1 unit/minute (outlet)

    So, time taken by pipe 'Y' alone to empty 60% of the container = (100 × 0.6) ÷ 1 = 60 minutes

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