JEE Main & Advanced Mathematics Statistics Question Bank Critical Thinking

  • question_answer
    The average of n numbers \[{{x}_{1}},\,{{x}_{2}},\,{{x}_{3}},\,......,\,{{x}_{n}}\] is M. If \[{{x}_{n}}\] is replaced by \[{x}'\], then new average is                 [DCE 2000]

    A)                 \[M-{{x}_{n}}+{x}'\]         

    B)             \[\frac{nM-{{x}_{n}}+{x}'}{n}\]

    C)                 \[\frac{(n-1)M+{x}'}{n}\]   

    D)                 \[\frac{M-{{x}_{n}}+{x}'}{n}\]

    Correct Answer: B

    Solution :

                    \[M=\frac{{{x}_{1}}+{{x}_{2}}+{{x}_{3}}......{{x}_{n}}}{n}\]                         i.e., \[\underset{n}{\mathop{\underline{\begin{matrix}    nM  \\    nM-{{x}_{n}}  \\    nM-{{x}_{n}}+{x}'  \\ \end{matrix}}}}\,\begin{matrix}    =  \\    =  \\    =  \\ \end{matrix}\underset{n}{\mathop{\underline{\begin{matrix}    {{x}_{1}}+{{x}_{2}}+{{x}_{3}}+......{{x}_{n-1}}+{{x}_{n}}  \\    {{x}_{1}}+{{x}_{2}}+{{x}_{3}}+......{{x}_{n-1}}\ \ \ \ \   \\    {{x}_{1}}+{{x}_{2}}+{{x}_{3}}+......{{x}_{n-1}}+{x}'  \\ \end{matrix}}}}\,\] \ New average\[=\frac{nM-{{x}_{n}}+{x}'}{n}\].            


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