I have a good one.
There are three kids, really smart kids. Their father wants to put them to the test to see who is the smartest. The father tells each kid that he is putting either a black dot on their foreheads or a red dot on their foreheads. If one child sees AT LEAST one black dot on someone else's forehead, he is to raise his hand. So he puts them in a room and asks them to find out what color they have on their forehead. How does one figure it out?
There are no tricks like a mirror or smudging it, they figured it out by logic.
