$v_{od}=\frac{v_d}{f_{od}}\left(f_0-f_{od}\right)$

$v_{zb}=\frac{v_d}{f_{zb}}\left(f_{zb}-f_0\right)$

$\frac{v_{od}}{v_{zb}}=\frac{\frac{v_d}{f_{od}}\left(f_0-f_{od}\right)}{\frac{v_d}{f_{zb}}\left(f_{zb}-f_0\right)}$

$\frac{v_{od}}{v_{zb}}=\frac{\cancel{v_d}}{f_{od}}\cdot \frac{f_{zb}}{\cancel{v_d}}\cdot \frac{f_0-f_{od}}{f_{zb}-f_0}$

$\frac{v_{od}}{v_{zb}}=\frac{f_{zb}}{f_{od}}\cdot \frac{f_0-f_{od}}{f_{zb}-f_0}$

$\frac{v_{od}}{v_{zb}}=\frac{520\cancel{\mathrm{Hz}}}{480\cancel{\mathrm{Hz}}}\cdot \frac{500\mathrm{Hz}-480\mathrm{Hz}}{520\mathrm{Hz}-500\mathrm{Hz}}=\frac{520}{480}\cdot \frac{20\cancel{\mathrm{Hz}}}{20\cancel{\mathrm{Hz}}}\approx 1,08$