Five liverpool players Daniel Agger, Steven Gerrard, Nuri Sahin, Luis Suarez, and Raheem Sterling have a dot mark in their forehead.
They can't see the dot on their own forehead, but can see the ones on others.
The owner of WHITE dot is an honest person and will never lie, while the owner of BLACK dot always tell the lie.
This is the statement from Daniel Agger, Steven Gerrard , Nuri Sahin and Raheem Sterling:
Daniel Agger: 'I see 3 whites and 1 black'
Steven Gerrard: 'I see 4 black'
Nuri Sahin: 'I see 3 black and 1 white'
Raheem Sterling: 'I see 4 white'
What color is the dot on each Daniel Agger, Steven Gerrard, Nuri Sahin, Luis Suarez, Raheem Sterling forehead?
Solution:
Daniel Agger, Steven Gerrard, Nuri Sahin, and Raheem Sterling stated a contradiction statement, so only one of them can said the truth.
We don't know yet where Luis Suarez stands, it's still possible that he has black or white color.
Thus, the maximum possibility of white dots are 2, that is Luis Suarez and 1 of Daniel Agger Steven Gerrard Nuri Sahin, and Raheem Sterling.
Daniel Agger and Raheem Sterling obviously told the lie, as they said there are 3 and 4 person has white dot, which leave us Steven Gerrard and Nuri Sahin .
Assuming Steven Gerrard is white, then he must be telling the truth that he saw 4 black dots, which makes Nuri Sahin a liar. This is an impossible situation, since Nuri Sahin saw 3 black and 1 white (Nuri Sahin has to be a liar, so there must be more than 1 white, meaning it's impossible Steven Gerrard saw 4 blacks).
The only possibility is Nuri Sahin told the truth.
So, Daniel Agger Steven Gerrard Raheem Sterling have black dots, while Nuri Sahin and Luis Suarez have white dots.