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    Question

    Three pipes are connected to a cistern such that pipes A

    and B can fill the cistern in 12 minutes and 18 minutes respectively, and pipe C can empty the cistern in 24 minutes. If all the pipes are opened together and pipe B is closed after a certain time, the total time taken to fill the cistern is 15 minutes. Find after how many minutes pipe B should be closed.
    A 12 mins 45 Secs Correct Answer Incorrect Answer
    B 6 mins 75 secs Correct Answer Incorrect Answer
    C 10 mins 25 secs Correct Answer Incorrect Answer
    D 18 mins 20 secs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ, 15/12 + x/18 – 15/24 = 1 (90 + 4x – 45) /72 = 1 45 + 4x = 72 4x = 27 x = 6.75 or 6 mins 75 secs

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