JEE Main & Advanced Mathematics Statistics Question Bank Mock Test - Statistics

  • question_answer
    Let\[{{x}_{1}},{{x}_{2}},{{x}_{3}},{{x}_{4}}\]and\[{{x}_{5}}\]be the observations with mean m and standard deviation s. The standard deviation of the observations \[k{{x}_{1}},\]\[k{{x}_{2}},\]\[k{{x}_{3}},\]\[k{{x}_{4}},\]and \[k{{x}_{5}},\] is

    A) \[k+s\]  

    B) s/k

    C) ks        

    D) s

    Correct Answer: C

    Solution :

    [c] Here, \[m=\frac{\Sigma {{x}_{i}}}{5},\,s=\sqrt{\frac{\Sigma x_{i}^{2}}{5}-{{\left( \frac{\Sigma {{x}_{i}}}{5} \right)}^{2}}}\] For observations \[k{{x}_{1}},k{{x}_{2}},k{{x}_{3}},k{{x}_{4}},k{{x}_{5}},\] \[SD=\sqrt{\frac{{{k}^{2}}\Sigma x_{i}^{2}}{5}-{{\left( \frac{k\Sigma {{x}_{i}}}{5} \right)}^{2}}}\] \[=\sqrt{\frac{{{k}^{2}}\Sigma x_{i}^{2}}{5}-{{k}^{2}}{{\left( \frac{\Sigma {{x}_{i}}}{5} \right)}^{2}}}\] \[=k\sqrt{\frac{\Sigma x_{i}^{2}}{5}-{{\left( \frac{\Sigma {{x}_{i}}}{5} \right)}^{2}}}=ks\]


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