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    Question

    Two pipes A and B can fill a tank in 24 minutes and 30

    minutes respectively, while a third pipe C can empty it in 40 minutes. If all three pipes are opened together, in how much time will the tank be filled?
    A 20 minutes Correct Answer Incorrect Answer
    B 18 minutes Correct Answer Incorrect Answer
    C 22 minutes Correct Answer Incorrect Answer
    D 24 minutes Correct Answer Incorrect Answer

    Solution

    Work done by A in 1 minute = 1/24 Work done by B in 1 minute = 1/30 Work done by C in 1 minute = -1/40 Net work done in 1 minute = 1/24 + 1/30 - 1/40 = 6/120 = 1/20 Time to fill the tank = 1 / (1/20) = 20 minutes Correct answer: a) 20 min

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