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    Question

    Pipe A fills a tank in 12 h; Pipe B in 15 h; Pipe C

    empties it in 10 h. All three opened together. After x hours, C is closed and tank gets full in 2 more hours. Find x.
    A 14 hrs Correct Answer Incorrect Answer
    B 11 hrs Correct Answer Incorrect Answer
    C 22 hrs Correct Answer Incorrect Answer
    D 32 hrs Correct Answer Incorrect Answer

    Solution

    ATQ,

    Rates: A=1/12, B=1/15, C=тИТ1/10.

    Net with C: 1/12 + 1/15 тИТ 1/10 = (5 + 4 тИТ 6)/60 = 3/60 = 1/20. Without C: 1/12 + 1/15 = (5 + 4)/60 = 9/60 = 3/20. Let x hours at 1/20, then 2 hours at 3/20 equals 1 tank. x┬╖(1/20) + 2┬╖(3/20) = 1 тЗТ x/20 + 6/20 = 1 тЗТ x/20 = 14/20 тЗТ x = 14. Answer: 14 hours.

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