Hiv infection among intravenous drug users. Found that 40% light users and 55% were heavy users were HIV positive.
1) Suppose we have a group of 10 light users and 10 heavy users. What is the probability that exactly 3 of 20 users are HIV positive.
2) Probability that at least 4 of the 20 users are HIV positive?
3) Is the distribution of the nmber of HIV possitive among the 20 users binomial? Why or Why not?