At this point in the party everyone is seated in a circle and must guess the colour of their own hat. If they do they get 100 dollars.
Every person can make a guess of yellow, red or blue and nothing else. Every person gets two such guesses but these can be made in any order. (That is one need not make both his guesses one right after the other.)
In order to win with one of your two guesses you must say the colour of your own hat. How can every person guarantee themselves the money? (How can they have a 100% chance of guessing the colour of their hat correctly?)