Three married couples (6 guests altogether) attend a dinner party. They sit at a round
table randomly in such a way that each outcome is equally likely. What is the probability
that somebody sits next to his or her spouse?
Hint. Label the seats, the individuals, and the couples. There are 6! = 720 seating arrange-
ments altogether. Apply inclusion-exclusion to the events Ai = {ith couple sit next to each other},
i = 1, 2, 3. Count carefully the numbers of arrangements in the intersections of the Ais.