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    Question

    Pipe β€˜A’ takes 30 minutes to fill a tank. Pipe

    β€˜B’ takes 40 minutes to empty the same tank. If pipe β€˜B’ is opened 20 minutes after pipe β€˜A’, then find the total time taken to fill the tank in this manner.
    A 61 minutes Correct Answer Incorrect Answer
    B 63 minutes Correct Answer Incorrect Answer
    C 64 minutes Correct Answer Incorrect Answer
    D 60 minutes Correct Answer Incorrect Answer
    E 70 minutes Correct Answer Incorrect Answer

    Solution

    Let the capacity of the tank be β€˜120’ litres {LCM (30, 40)} Efficiency of pipe β€˜A’ = (120/30) = 4 litres/minute Efficiency of pipe β€˜B’ = (120/40) = 3 litres/minute Quantity of water filled by pipe β€˜A’ in 20 minutes = 4 Γ— 20 = 80 litres Quantity of water to be filled = 120 – 80 = 40 litres Time taken by pipe β€˜A’ and β€˜B’ together to fill 40 litres of water = {40/(4 – 3)} = 40 minutes Total time taken = 20 + 40 = 60 minutes

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