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    Question

    Pipe 'P' and 'Q' can fill a tank in 50 minutes and 1

    hour 40 minutes respectively. 'P' is opened alone. After 20 minutes, 'P' is closed and 'Q' is opened. Find the time taken by 'Q' to fill the remaining tank.
    A 60 minutes Correct Answer Incorrect Answer
    B 70 minutes Correct Answer Incorrect Answer
    C 80 minutes Correct Answer Incorrect Answer
    D 90 minutes Correct Answer Incorrect Answer
    E 100 minutes Correct Answer Incorrect Answer

    Solution

    Let the total capacity of tank be 200 litres (LCM of 50 and 100) Efficiency of 'P' = (200/50) = 4 litres/minute Efficiency of 'Q' = (200/100) = 2 litres/minute Tank filled by 'P' = 4 × 20 = 80 litres Remaining part of the tank = 200 − 80 = 120 litres Required time = (120/2) = 60 minutes 

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