Required Mathematical Intelligence

Chapter 33 Black and White Foreheads
There are five people A, B, C, D, and E.Each of them fastened a round white or black medal to his forehead.Each could see the cards fastened to the foreheads of the other four, but none of his own.If a person's disc is white, what he says is true; if his disc is black, what he says is false.Here's what they said:

A said: I see three white cards and one black card.

B said: I see four black cards.

C said: I see one white card and three black cards.

E says: I see four white cards violated.

What is the color of the medals each of them tie?

[Answer: Look at E first, if it is true, then everyone else should say...

If you look at B again, if... (Note: the words of the black card player will not be correct), then look at A, then look at C, D must be...

A, B, E are black cards. C and D are white cards. ]
(End of this chapter)