When a gas is diffusing through air in a diffusion channel, the diffusion rate is the number of gas atoms per second diffusing from one end of the channel to the other end. The faster the atoms move, the greater is the diffusion rate, so the diffusion rate is proportional to the rms speed of the atoms. The atomic mass of ideal gas $A$ is $2u,$ and that of ideal gas $B$ is $5u.$ For diffusion through the same channel under the same conditions, find the ratio of the diffusion rate of gas $A$ to the diffusion rate of gas $B.$

$\frac{R_A}{R_B}=$ Number $$ Units $$