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    Question

    A tank is filled by two pipes A and B in 12 minutes and

    15 minutes, respectively. Another pipe C can empty the tank in 10 minutes. If all three pipes are opened together, how long will it take to fill the tank?
    A 60 minutes Correct Answer Incorrect Answer
    B 30 minutes Correct Answer Incorrect Answer
    C 20 minutes Correct Answer Incorrect Answer
    D 24 minutes Correct Answer Incorrect Answer

    Solution

    Work done by pipe A in 1 minute = 1/12 Work done by pipe B in 1 minute = 1/15 Work done by pipe C in 1 minute = -1/10 Net work done in 1 minute = (1/12 + 1/15 - 1/10) = 3/60 Time taken to fill the tank = 1 ÷ 1/20 = 20 minutes Correct answer: c) 20 minutes

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