JEE Main & Advanced Mathematics Probability Question Bank Use of permutations and combinations in probability

  • question_answer
    A drawer contains 5 brown socks and 4 blue socks well mixed. A man reaches the drawer and pulls out 2 socks at random. What is the probability that they match

    A)            \[\frac{4}{9}\]                          

    B)            \[\frac{5}{8}\]

    C)            \[\frac{5}{9}\]                          

    D)            \[\frac{7}{12}\]

    Correct Answer: A

    Solution :

                       Out of 9 socks, 2 can be drawn in \[{}^{9}{{C}_{2}}\] ways.                    Two socks drawn from the drawer will match if either both are brown of both are blue. Therefore favourable number of cases is \[{}^{5}{{C}_{2}}+{}^{4}{{C}_{2}}.\]                      Hence the required probability \[=\frac{{}^{5}{{C}_{2}}+{}^{4}{{C}_{2}}}{{}^{9}{{C}_{2}}}=\frac{4}{9}.\]


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