Consider the Ehrenfest urn model in which M molecules are distributed among two urns, and at each time point one of the molecules is chosen at random and is then removed from its urn and placed in the other one. Let X, denote the number of molecules in urn 1 after the nth switch and let , =E[X]. Show that (i) +11+ (1 - 2/M)un (ii) Use (i) to prove that M = H-+(-2) (Ex-M) E[X]