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    Question

    Pipes D and E alone can fill a tank in 5 hours and 3 hours

    respectively. When both pipes along with pipe F, an outlet pipe, are opened together, 1/2 of the tank gets filled in 60 minutes. Find the time taken by pipe F to empty a completely filled tank.
    A 20 hours Correct Answer Incorrect Answer
    B 25 hours Correct Answer Incorrect Answer
    C 30 hours Correct Answer Incorrect Answer
    D 35 hours Correct Answer Incorrect Answer
    E 40 hours Correct Answer Incorrect Answer

    Solution

    Let the total capacity of the tank be 15 litres.
    Efficiency of Pipe 'D' = 15 / 5 = 3 litres/hour
    Efficiency of Pipe 'E' = 15 / 3 = 5 litres/hour
    Let pipe 'F' empties the tank with an efficiency of 'm' litres/hour.
    Tank filled in 60 minutes = (1/2) × 15 = 7.5 litres
    ATQ,
    (3 + 5 - m) × (60/60) = 7.5
    (8 - m) × 1 = 7.5
    8 - m = 7.5
    m = 0.5 litres/hour
    Time taken by F to empty the tank = 15 / 0.5 = 30 hours

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