A group of 25 people consists of knights, knaves and liars. Each person was asked "Are you a
knight?", and 17 responded yes. Each person was then asked "Are you a knave?", and 12 responded yes.
And finally each person was asked "are you a liar?", and 8 responded yes.
How many knights, knaves and liars are in the group?
This is a really good one. Makes you stop and think, and has an elegant answer. I especially like that the people who answered Yes to the second question are a subset of those who answered Yes to the first, and those who responded Yes to the third were a subset of those who responded Yes to the second.