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    Question

    Pipes P and Q alone can fill a tank in 6 hours and 3

    hours respectively. When both pipes along with pipe R, an outlet pipe, are opened together, 2/5 of the tank gets filled in 60 minutes. Find the time taken by pipe R to empty a completely filled tank.
    A 6 hours Correct Answer Incorrect Answer
    B 8 hours Correct Answer Incorrect Answer
    C 10 hours Correct Answer Incorrect Answer
    D 12 hours Correct Answer Incorrect Answer

    Solution

    Let the total capacity of the tank be 30 litres.
    Efficiency of Pipe 'P' = 30 / 6 = 5 litres/hour
    Efficiency of Pipe 'Q' = 30 / 3 = 10 litres/hour
    Let pipe 'R' empties the tank with an efficiency of 'm' litres/hour.
    Tank filled in 60 minutes = (2/5) × 30 = 12 litres
    ATQ,
    (5 + 10 - m) × (60/60) = 12
    (15 - m) × 1 = 12
    15 - m = 12
    m = 3 litres/hour
    Time taken by R to empty the tank = 30 / 3 = 10 hours

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