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

  • question_answer
    The mean of five observations is 4 and their variance is \[5\cdot 2\]. If three of these observations are 2, 4 and 6, then the other two observations are

    A) 3 and 6

    B) 2 and 6

    C) 5 and 8

    D) 1 and 7

    Correct Answer: D

    Solution :

    [d] Let the other two observations be ?a? and ?b? \[\therefore \] mean \[=\frac{2+4+6+a+b}{5}\Rightarrow 4=\frac{12+a+b}{5}\] \[\Rightarrow a+b=8;\] Variance \[=\frac{1}{n}\sum{{{x}^{2}}}-{{x}^{-2}}=5.2\] \[\Rightarrow \frac{1}{5}\left( 4+16+36+{{a}^{2}}+{{b}^{2}} \right)-16=5.2\Rightarrow {{a}^{2}}+{{b}^{2}}\]\[=50\] From the options, it is clear that the two observations are 1 and 7.


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