Root-mean-square Distance

The average distance x_rms that a molecule travels  by diffusion is proportional to the square root of time:

x_rms = √ (2Dt)

where
x_rms stands for the root-mean-square distance and is the statistical average for the process,
D is the diffusion constant for the particular molecule in a specific medium. 

t = x_rms² /  (2D)

t₁ = x_1rms² /  (2D)

t₂ = x_2rms² /  (2D)

t₂  /  t₁ = x_2rms²  /   x_1rms²

t₂ = t₁ x_2rms²  /   x_1rms²