JEE Main & Advanced Mathematics Statistics Question Bank Self Evaluation Test - Statistics

  • question_answer
    The range of a random variable x is \[\{1,2,3,...\}.\] If \[P(x=r)=\frac{1}{{{2}^{r}}}\], then the mean of the distribution is

    A) 8

    B) 16

    C) 1

    D) 2

    Correct Answer: D

    Solution :

    [d] Mean \[E(x)=\Sigma rP(r)=\Sigma r.\frac{1}{{{2}^{r}}}\] \[\therefore E(x)=\frac{1}{2}+\frac{2}{{{2}^{2}}}+\frac{3}{{{2}^{3}}}+...\] \[\frac{1}{2}E(x)=\frac{1}{{{2}^{2}}}+\frac{2}{{{2}^{3}}}+...\] \[\therefore \frac{1}{2}E(x)=\frac{1}{2}+\frac{1}{{{2}^{2}}}+\frac{1}{{{2}^{3}}}+...=\frac{1/2}{1-1/2}\] \[\therefore E(x)=2\]


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