Negative Binomial nd The 2 most common letter in English is I with about 8% occurrence.th a) What is the probability that you get exactly 3 Is on the 12 character? b) What is the expected number of characters to get 3 Is? d) Poisson Distribution A Help Desk Employee closes 3 tickets per hour on average. a) What is the probability that 2 or 3 are completed in one hour? b) What is the probability fewer than 4 are completed?.