A king wants an advisor and comes to ask the 3 wisest sages.
He blindfolds them and put the hats on their head. Afterwards,
the king takes off their blindfolds. He tells them that
their hat is either blue or white. He tells them that whoever
can deduce the color of their hat will be his next advisor.
Also he tells them that at least one of the sages will be
wearing a blue hat. The sages can all see each other's hats
except of course, their own. Sage A sees that the other 2 are
wearing blue hats.
For hours no one spoke, then Sage A stands up and tells the
king the colour of his hat. What color is it and how does he know?