Successive customers visit a retail store. Each customer acts independent of others. The probability that a customer buys something is 0.8, so with 0.2 probability, the customer does not buy anything. We observe 5 customers at the store. Let X be the number among them who buy something from the store. Clearly X is a random variable, with possible values 0, 1, 2, 3, 4, or 5. What is the distribution of X? What is the mean of X? What is the standard deviation of X? What is the probability that X is 3 or more?