Edmund's Brainteasers
Problem 4
Problem 4: The five hats
Ian Michael told me about the following problem. Thanks Ian!
At the All Saints' Annual Party Marie-Louise, David and Gavin play a game. Jonathan has five hats, 3 black and two blue. Marie-Louise, David and Gavin shut their eyes and Jonathan puts a hat on each of their heads. They are told to open their eyes and look at the colour of the hats worn by the other two. Marie-Louise sees that David and Gavin both have a black hat. Jonathan offers a prize to the first who can tell him the colour of their hat. After a few moments when each is deep in thought, Marie-Louise answers that her hat is black and she wins the prize. How did she work it out?