Men with Hats: There are 4 men each wearing either a black or a white hat. They are standing in rising water, cannot move and can only look forward. Between A and B is a brick wall which they cannot see through. They know that between them are 4 hats of which 2 are black and 2 are white, but they do not know which colour they are wearing. In order to stop the level of water rising and drowning, one of them must call out correctly which colour hat he is wearing. They are not allowed to talk to each other and have 10 minutes to fathom it out. Question: Which one of them call out, and how does he work out which colour he is wearing?
