Some Abstract Thought!?

For clarity sake lets call the guys A, B and C. "A" assumes his hat is black. "B" raises his hand as he sees a red hat. "A" can see that C's hat is red and according to his (A's) assumption his hat is black therefor C should leave the room, but C doesn't as C can see A's hat is red. Thus A knows his hat is red and leaves the room.

Since you didn't specify I am assuming that the guys can walk around the room. In this case, guy A (the one who left the room) simply waited for, or forced the other two guys into this sort of setup (arrows represent direction that person is facing):

A=> <=B C=>

Then (with person C clearly out of sight of B) A observed B raising his hand and deduced that his own hat was red.

god knows i can tell you that all the answers so far are wrong

1that other 2 were siting down thinking that theirs were black, doesnt mean he has a red hat

2that the other 2 have red hats doesnt mean he has a red one

3 if the other 2 had rose their hand , it still doesnt show that he has a red hat (as they could be raising their hands seeing each others hats)

unless they paired up which probably isnt allowed as they are not allowed to communicate

youve beaten me

EDit: i just got an idea he saw the reflection of his hat in the eye of another hat wearer!

all the hats were red and they said if u can guess the color of your hat u can leave and if u see a red hat raise your hand and so he did

when they were both looking at him, they raised their hands.

another theory, he saw that the other hats were red and figured his was too?

He told the other guys to turn around one at a time, then watched to see if they raised their hands.

The other two were sitting thinking their hat may be black.

This is a very old puzzel in our place.India(Bangalore)

By taking a peek and he has eyes in the back of his head.

he raised his hand maybe

no clue, tell me when you choose the best answer