A system consists of two types of gas molecules $A$ and $B$ having the same number density $2\times {10}^{25} {\mathrm{m}}^{-3}$. The diameter of $A$ and $B$ are $10A$ and $5A$ respectively. They suffer collisions at room temperature. The ratio of average distance covered by the molecule $A$ to that of $B$ between two successive collisions is ___________$\times {10}^{-2}$