Riddle: The Dinner Party
You and your wife organize a dinner party. You invite four other husband-wife couples. You and your wife don't necessarily know everyone you invited. Once everyone is at the party, the people who don't know each other yet shake hands with each other. You can assume that everyone knows their own wife/husband, and that noone shakes their own hand.
After this happens, you ask each person, except for yourself, how many people they shook hands with. Everybody tells you a different number.
How many people did your wife shake hands with?
Yes, this riddle is possible. If everbody shook hands with a different number of people, then the most any person shook hands with was 8 people, and in fact, a single person must have shaken hands with exactly 8 people. Figure out exactly who this person did - and didn't - shake hands with. Then go from there.