This problem uses the statistical postulate to address diffusion. Consider eight particles, 4 black and 4 white. The particles are in a liquid with two halves separated by a permeable membrane, so each particle can be either on the left or the right of the membrane. According to the statistical postulate, every arrangement of the 8 particles is equally likely. Arrangements can be summarized according to which particles are on the left and which on the right, with the membrane represented by a vertical line |. Some possible arrangements are: , BWBW|BWBW, and WWW|BBW. How many different arrangements are there?