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    Question

    Two inlet pipes 'A' and 'B' can fill an empty tank in 30

    minutes and 40 minutes, respectively. Another outlet pipe 'C' can empty the tank in 120 minutes. If all the three pipes are opened together, then find the time taken by them to fill the tank.
    A 18 minutes Correct Answer Incorrect Answer
    B 19 minutes Correct Answer Incorrect Answer
    C 20 minutes Correct Answer Incorrect Answer
    D 21 minutes Correct Answer Incorrect Answer
    E 22 minutes Correct Answer Incorrect Answer

    Solution

    Let the total capacity of the tank be 120 litres (LCM of 30, 40, and 120).
    Efficiency of 'A' = 120 ├╖ 30 = 4 litres/minute
    Efficiency of 'B' = 120 ├╖ 40 = 3 litres/minute
    Efficiency of 'C' = 120 ├╖ 120 = -1 litre/minute
    Required time = 120 ├╖ (4 + 3 - 1) = 120 ├╖ 6 = 20 minutes

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