N people arrive separately to a professional dinner. Upon arrival, each person looks to se...

N people arrive separately to a professional dinner. Upon arrival, each person looks to see if he or she has any friends among those present. That person then sits either at the table of a friend or at an unoccupied table if none of those present is a friend. Assuming that eachof  pairs of people is, independently, a pair of friends with probability p, find the expected number of occupied tables.