JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2011

  • question_answer
        A bag contains 12 pairs of socks, 4 socks are picked up at random. Then, the probability that there is at least one pair is

    A)  \[\frac{41}{161}\]                                           

    B)  \[\frac{120}{161}\]

    C)  \[\frac{21}{161}\]                                           

    D)  None of these

    Correct Answer: A

    Solution :

                    Total number of ways of selecting 4 socks \[{{=}^{24}}{{C}_{1}}{{\times }^{23}}{{C}_{1}}{{\times }^{22}}{{C}_{1}}{{\times }^{21}}{{C}_{1}}\] \[=24\times 23\times 22\times 21\] The total number of ways of selecting no pair \[=24\times 22\times 20\times 18\] \[\therefore \]Required probability \[=1-P\](no one getting a pair)                 \[=1-\frac{24\times 22\times 20\times 18}{24\times 23\times 22\times 21}=1-\frac{120}{161}\]                 \[=\frac{41}{161}\]


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