1. The problem statement, all variables and given/known data A test tube of cylindrical shape having a length of 10 cm and a diameter of 2 cm contains 20 * 10 ^23 molecules (molecular size d = 3 * 10^-10 m). What is the mean free path of these molecules?? 2. Relevant equations λ = 1/ pi * d^2 * n 3. The attempt at a solution This is an equation I have never used before and my text book doesn't help with either. I tried to solve it by: 1 / pi * (2 cm)^2 * (20 * 10^23 / 3*10^-12 cm) I haven't ever done something like it before, am I on the right track with this?