This is probably my favorite puzzle. It uses logic, but it's not one of those "logic table" puzzles which i dislike immensely. What is this type of puzzle called and are there more like it that are not just variants?
Three children are playing on the beach and all three have mud on their foreheads. An old man walks by and asks them, “After looking at both of your friends foreheads, raise your hand if one or both of them have mud on their foreheads.“ All three children look at both their friends and raise their hands.
He then asks, “For a dollar, without touching your own forehead or looking in a mirror or anything similar, tell me if you have mud on your own forehead, and how you know that.” All three children are bewildered. Finally, one raises his hand and says, “i have mud on my forehead.” He explains how he knew this and receives the dollar.
What was his reasoning?
Note: The old man and the children are honest, able to employ logic, and want the dollar.