Let Y be the number of calls to a particular hotline within 10 min. Suppose Y is a Poisson random variable with mean of 3. Find the probability that there are at most 4 calls given that there are already 2 calls within the 10 min.
I'm not really sure how to go about solving this. Am I supposed to be looking at this in terms of a binomial random variable? If not, then how would I set up the conditional probability?