Persons entering a blood bank are such that 1 in 3 have type O+ blood and 1 in 18 have type O− blood. Consider three randomly selected donors for the blood bank. Let X denote the number of donors with type O+ blood and Y denote the number with type O− blood. Find the probability distributions for X and Y. Also find the probability distribution for Z = X + Y, the number of donors who have type O blood. (Round your answers to four decimal places.)