JEE Main & Advanced Mathematics Question Bank Critical Thinking

  • question_answer
    Six boys and six girls sit in a row. What is the probability that the boys and girls sit alternatively               [IIT 1979]

    A)                 \[\frac{1}{462}\]  

    B)                 \[\frac{1}{924}\]

    C)                 \[\frac{1}{2}\]       

    D)                 None of these

    Correct Answer: A

    Solution :

               Let \[n=\] total number of ways \[=12\,!\]            and \[m=\] favourable number of ways \[=2\times 6\,!\,.\,6\,!\]            Since the boys and girls can sit alternately in \[6\,!\,\,.\,\,6\,!\] ways if we begin with a boy and similarly they can sit alternately in \[6\,!\,\,.\,\,6\,!\] ways if we begin with a girl                                 Hence required probability \[=\frac{m}{n}=\frac{2\times 6\,!\,\,.\,\,6\,!}{12\,!}=\frac{1}{462}\].


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