Shown above are four men buried up to their necks on the ground. They cannot move and can only look forward. Between A and B is a brick wall which cannot be seen through. They know that between them are four hats, two black and two white, but they do not know what colour they are wearing.
In order to avoid being shot one of them must call out to the executioner the colour of his hat. If he gets it wrong, everyone will be shot. They are not allowed to talk to each other and have ten minutes to fathom it out.
After one minute:
Q: Which of them calls out?
Q: Why is he 100% certain of the colour of his hat?
This is not a trick question.
There are no outside influences nor any other ways of communicating. They cannot move and are buried in a straight line. A and B can see only their respective sides of the brick wall, C can see B, and D can see B and C.
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