The probability it leaves is 0.3 each second, and the probability it returns is 0.2 each second.
The following probabilities describe molecules that can hop into and out of a cell. For each, find a discrete-time dynamical system for the probability that the molecule is inside. Find the probability that a molecule that begins inside is inside at t = 2, and the probability that a molecule that begins outside is inside at t = 2. Compute the equilibrium, and use it to estimate how many out of 100 molecules would be inside after a long time.