A system consists of two types of gas molecules A and B having same number density 2 $\times$ 10²⁵/m³. The diameter of A and B are 10 $\mathop A\limits^o $ and 5 $\mathop A\limits^o $ respectively. They suffer collision at room temperature. The ratio of average distance covered by the molecule A to that of B between two successive collision is ____________ $\times$ 10^$-$2