$\sum\limits_{i=1}^{10}{({{x}_{i}}}-\overline{x}{{)}^{2}}=\sum\limits_{i=1}^{10}{{{x}^{2}}-2\overline{x}}\sum\limits_{i=1}^{10}{x+\sum\limits_{i=1}^{10}{{{\overline{x}}^{2}}}}=\sum\limits_{i=1}^{10}{{{x}^{2}}}-10{{\overline{x}}^{2}}$ ${{\delta }^{2}}=\frac{\sum {{x}^{2}}}{10}-{{\bar{x}}^{2}}=\frac{14/4}{10}=1/44\Rightarrow \delta =1/2$ چون $cv=\frac{\delta }{{\bar{x}}}$ پس $\frac{1/2}{{\bar{x}}}=%4$ یا $\overline{x}=30$