$\overline{x}=\frac{33+21+51}{5}=21$                   $x-\overline{x}=-6,-3,0,3,6$ ${{\delta }^{2}}=\frac{36+9+45}{5}=18\Rightarrow \delta =3\sqrt{2}$ پس $CV=\frac{3\sqrt{2}}{21}=\frac{1/4}{7}=0/2$