Question 189
There are some boys and some girls at a party. A set of boys is said to be *sociable* if every girl at the party knows at least one boy in that set, and similarly a set of girls is said to be *sociable* if every boy at the party knows at least one girl in that set.
Suppose that the number of sociable sets of boys is odd. Prove that the number of sociable sets of girls is also odd.
NOTE: Acquaintance is mutual.
Suppose that the number of sociable sets of boys is odd. Prove that the number of sociable sets of girls is also odd.
NOTE: Acquaintance is mutual.