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    Question

    Pipe ‘A’ takes 20 minutes to fill a tank. Pipe

    ‘B’ takes 35 minutes to empty the same tank. If pipe ‘B’ is opened 17 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 24 minutes Correct Answer Incorrect Answer

    Solution

    Let the capacity of the tank be ‘140’ litres {LCM (20, 35)} Efficiency of pipe ‘A’ = (140/20) = 7 litres/minute Efficiency of pipe ‘B’ = (140/35) = 4 litres/minute Quantity of water filled by pipe ‘A’ in 17 minutes = 17 × 7 = 119 litres Quantity of water to be filled = 140 – 119 = 21 litres Time taken by pipe ‘A’ and ‘B’ together to fill 21 litres of water = {21/(7 – 4)} = 7 minutes Total time taken = 17 + 7 = 24 minutes

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