JEE Main & Advanced Mathematics Probability Question Bank Self Evaluation Test - Probability-I

  • question_answer
    Let X be a set containing n elements. If two subsets A and B of X are picked at random, the probability that A and B have the same number of elements, is

    A) \[\frac{^{2n}{{C}_{n}}}{{{2}^{2n}}}\]

    B) \[\frac{1}{^{2n}{{C}_{n}}}\]

    C) \[\frac{1\cdot 3\cdot 5...(2n+1)}{{{2}^{n}}n!}\]

    D) \[\frac{{{3}^{n}}}{{{4}^{n}}}\]

    Correct Answer: A

    Solution :

    [a] Required probability \[=\frac{\sum\limits_{r=0}^{n}{^{n}{{C}_{r}}{{\times }^{n}}{{C}_{r}}}}{{{2}^{n}}\times {{2}^{n}}}\] \[=\frac{C_{0}^{2}+C_{1}^{2}+C_{2}^{2}+...+C_{n}^{2}}{{{4}^{n}}}=\frac{^{2n}{{C}_{n}}}{{{2}^{2n}}}\]


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