How does a blind know the color of his hat?
There are totally 2 red hats and 3 white hats. There are 3 men A, B, C each have a hat on his head. A, B each can see other 2 mans' hats but cannot see his own hat. C is blind.
Now firstly A says he don't know the color of his hat.
And secondly B says he also don't know the color of his hat.
Finally after hearing what A and B said C says he knows the color of his hat.
What is the color of C's hat? How does C know?