[tex]Media \ proportionala=media \ geometrica= \sqrt{x \cdot y} \\ x= \frac{20}{7}; \ y= \frac{5}{63} ; \\ \Rightarrow \ \sqrt{ \frac{20}{7} \cdot \frac{5}{63} } = \sqrt{ \frac{100}{441} } = \frac{ \sqrt{100} }{ \sqrt{441} } =\boxed{ \frac{10}{21} }.[/tex]