Given, coefficient of variation $C_1=50$

and coefficient of variation $C_2=60$.

We have, ${\overline{x}}_1=30$ and ${\overline{x}}_2=25$

$\because C=\frac{\sigma }{\overline{x}}\times 100$

$50=\frac{{\sigma }_1}{30}\times 100$

$\Rightarrow {\sigma }_1=15$

and $60=\frac{{\sigma }_2}{25}\times 100$

$\Rightarrow {\sigma }_2=15$

$\therefore$ Required difference ${\sigma }_1-{\sigma }_2=15-15=0$