Assume there is a population of a given (even) size. One person is ‘infected’ in the beginning. During every ‘round’, everybody in the population pairs off and ‘interacts’ with her partner. If an infected person interacts with an uninfected person, the uninfected person is then infected. If two infected people interact, there is no change. Let’s say my favorite guy in this population is Bob. After n rounds, what is the probability Bob is infected? Further, if an infected person interacts with an uninfected person, assume there is a known probability, p, that the uninfected person will get infected. What is the new probability Bob will be infected? You can probably guess what this problem is attempting to model. I’m guessing the answer is recursive, so do your best.