JEE Main & Advanced Mathematics Probability Question Bank Binomial distribution

  • question_answer
    A coin is tossed 2n times. The chance that the number of times one gets head is not equal to the number of times one gets tail is                                       [DCE 2002]

    A)                 \[\frac{(2n!)}{{{(n!)}^{2}}}{{\left( \frac{1}{2} \right)}^{2n}}\]               

    B)                 \[1-\frac{(2n!)}{{{(n!)}^{2}}}\]

    C)                 \[1-\frac{(2n!)}{{{(n!)}^{2}}}\,.\,\frac{1}{{{4}^{n}}}\]            

    D)   None of these

    Correct Answer: C

    Solution :

               The required probability                   = 1 ? Probability of equal number of heads and tails                 \[=1-{{\,}^{2n}}{{C}_{n}}{{\left( \frac{1}{2} \right)}^{n}}{{\left( \frac{1}{2} \right)}^{2n-n}}=1-\frac{(2n)\,!}{n\,!\,n\,!}{{\left( \frac{1}{4} \right)}^{n}}=1-\frac{(2n)\,!}{{{(n\,!\,)}^{2}}}\cdot \frac{1}{{{4}^{n}}}\].


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