This is simple for you, hard for me.... I really need to know how to do a question like this for a course I am taking. Can you help???? Out of 2 million hay fever sufferers in Canada, 82% are allergic to ragweed. If a random sample of 7 hay fever sufferers is selected, a) what is the probability that 3 are allergic to ragweed? b) What is the probability that 1 is allergic to ragweed? What is the formula???
The basic idea is to use the binomial distribution with p=.82 and q=.18. That is expand (p+q)^{n} into powers of p (and q). Then the probability of exactly k yesses is {n,k}p^{k}q^{n-k}. I am using {n,k} to represent n!/k!(n-k)!. In your problem, n=7 and k=1 or k=3.