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

  • question_answer
    The mean of the series \[{{x}_{1}},{{x}_{2}},...{{x}_{n}}\] is \[\bar{X}\]. If \[{{x}_{2}}\] is replaced by \[\lambda ,\] then what is the new mean?

    A) \[\bar{X}-{{x}_{2}}+\lambda \]

    B) \[\frac{\bar{X}-{{x}_{2}}-\lambda }{n}\]

    C) \[\frac{\bar{X}-{{x}_{2}}+\lambda }{n}\]

    D) \[\frac{n\bar{X}-{{x}_{2}}+\lambda }{n}\]

    Correct Answer: D

    Solution :

    [d] Mean of series \[({{x}_{1}},{{x}_{2}},{{x}_{3}}...{{x}_{n}})\] \[\bar{x}=\frac{{{x}_{1}}+{{x}_{2}}+{{x}_{3}}+....{{x}_{n}}}{n}\] \[\Rightarrow {{x}_{1}}+{{x}_{2}}+{{x}_{3}}+...{{x}_{n}}=n\bar{x}\] Now we will replace \[{{x}_{2}}\] by so no. of elements in series will not change. New series will include \[\lambda \] and exclude \[{{x}_{2}}\] Hence new series sum: \[({{x}_{1}}+{{x}_{2}}+...{{x}_{n}})-{{x}_{2}}+\lambda =n\bar{x}+\lambda -{{x}_{2}}\] Now new mean \[=\frac{n\bar{x}+\lambda -{{x}_{2}}}{n}=\frac{n\bar{x}-{{x}_{2}}+\lambda }{n}\]


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