JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2010

  • question_answer
        The arithmetic mean of a set of observations is \[\overline{X}\]. If each observation is divided by a and then is increased by 10, then the mean of the new series is

    A)  \[\frac{\overline{X}}{\alpha }\]                                

    B)  \[\frac{\overline{X}+10}{\alpha }\]

    C)  \[\frac{\overline{X}+10\,\alpha }{\alpha }\]                       

    D)  \[\alpha \overline{X}+10\]

    Correct Answer: C

    Solution :

                    Let\[{{x}_{1}},{{x}_{2}},...{{x}_{n}}\]be n observations. Then, \[\overline{X}=\frac{1}{n}\Sigma {{y}_{i}}\] Let\[{{y}_{i}}=\frac{{{x}_{i}}}{\alpha }+10\](according to the given condition) Then,    \[\overline{Y}=\frac{1}{n}\Sigma {{y}_{i}}\]                 \[=\frac{1}{n}\Sigma \left( \frac{{{x}_{i}}}{\alpha }+10 \right)\]                 \[=\frac{1}{\alpha }\left( \frac{1}{n}\Sigma {{x}_{i}} \right)+\frac{1}{n}(10n)\]                 \[=\frac{1}{\alpha }\overline{X}+10\] \[\Rightarrow \]               \[\overline{Y}=\frac{\overline{X}+10\alpha }{\alpha }\]


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