Rebecca and her partner attend an evening party together with four other couples. During the initial mingling, everyone greets and shakes hands with those they hadn't met before.
Later in the evening Rebecca asks all nine other party-goers how many people they shook hands with, and she gets nine different answers.
How many people did Rebecca shake hands with?
Please note that everyone had met their partner prior to the party, and that no one shook hands with themselves.
Categories: graph theory