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    Question

    Pipe ‘A’ takes 10 minutes to fill a tank. Pipe

    ‘B’ takes 20 minutes to empty the same tank. If pipe ‘B’ is opened 5 minutes after pipe ‘A’, then find the total time taken to fill the tank in this manner.
    A 10 minutes Correct Answer Incorrect Answer
    B 12 minutes Correct Answer Incorrect Answer
    C 15 minutes Correct Answer Incorrect Answer
    D 17 minutes Correct Answer Incorrect Answer
    E 20 minutes Correct Answer Incorrect Answer

    Solution

    Let the capacity of the tank be ‘20’ litres {LCM (10, 20)} Efficiency of pipe ‘A’ = (20/10) = 2 litres/minute Efficiency of pipe ‘B’ = (20/20) = 1 litres/minute Quantity of water filled by pipe ‘A’ in 5 minutes = 5 × 2 = 10 litres Quantity of water to be filled = 20 – 10 = 10 litres Time taken by pipe ‘A’ and ‘B’ together to fill 10 litres of water = {10/(2 – 1)} = 10 minutes Total time taken = 5 + 10 = 15 minutes

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