Two planets have radii in the ratio x : y and density in the ratio m : n. The acceleration due to gravity ‘g’ is in the ratio

mx : ny

$g=\frac{GM}{R^2}=G \frac{\frac{4}{3} \pi R^3 \rho}{R^3}=G \frac{4}{3} \pi R \rho$

(As $\frac{R_1}{R_2}=\frac{x}{y} ; \frac{\rho_1}{\rho_2}=\frac{m}{n}$)

$\frac{g_1}{g_2}=\frac{G \frac{4}{3} \pi R_1 \rho_1}{G \frac{4}{3} \pi R_2 \rho_2}=\frac{R_1 \rho_1}{R_2 \rho_2}$

$=\frac{x}{y} \times \frac{m}{n}=\frac{mx}{ny}$