Question: A mixed group: means. A group of 20 children at a nursery school are exposed to whooping cough by playing with an infected child. Of these children 17 have been vaccinated and 3 have not.
(a) What is the distribution of the number of new infections among the 17 vaccinated children? What is the mean number of new infections?
(b) What is the distribution of the number of new infections among the 3 unvaccinated children? What is the mean number of new infections?
(c) Add your means from parts (a) and (b). This is the mean number of new infections among all 20 exposed children.