Here's a brainteaser:

[GaijinAndrew]

So there's this wise man which has an unknown number of apprentices. One day he gathers all of them and tells them: "Today I will separate the wise from the foolish." He brings out a bag of red balls and a bag of white balls (their number is also unknown). "Those which are wise will receive a red ball and those which are not will receive a white ball." after which he starts to put the balls on their heads. Catch is every apprentice can see the balls on the others heads but not his own. The master then says: "All of the wise men take a step further!" The apprentices start looking at each other but no one moves. The master repeats: "All of the wise men take a step further!" The apprentices have the same reaction. The same thing happens the third time, yet the fourth time when the master asks the wise men to move they do. And the master congratulates them.

How did the wise men know they had red balls on their heads?

 

[Deguasser]

because they all had red balls on their head.

 

[Les Awesome]

they asked each other

 

[Geekosaurus]

Because none of them had red balls on their heads. They all see that everybody has white balls on their heads so assume that they must be the only one with a red ball.

 

[Lilani]

They saw the balls as the master was pulling them out of the bag.

 

[Rakkana]

He doesn't seem very wise... >.>

I'm afraid I need proof.

Also how are the apprentices wise men? Which are they? Make your mind up!

 

[GaijinAndrew]

They are not allowed to talk to each other. And lets say you're an apprentice. You see everyone with red balls, how would you know you don't have a white ball on your head?

 

[Wrists]

Everyone looked at the people with red balls on their heads. they realised this and step forward. Or maybe they saw the ball before the master put it on their head.

 

[GaijinAndrew]

They became wise men if they had red balls on their head.

 

[burningdragoon]

After 3 times of being confused and looking at each other, the balls roll of their heads and they all see what ball was on their heads.

I'm not sure there is enough information given to answer this thing.

 

[cyce3]

Because the first three times he just says "al the wise me take a step forward" whereas the fourth time he asks the wise men to move. i.e. he individually asks those with the red balls o take a tep forward?

 

[Hlain]

They became wise men if they had red balls on their head.

Then the felt the enlightened and knew they were wise.

 

[CheesusCrust]

I have no idea, but I think it has something to do with the number of apprentices or you wouldn't go into the detail of not specifying the amount.

 

[Duffeknol]

It doesn't matter if they had white or red balls. Every man who is willing to 'take a step further' is a wise man.

 

[[.redacted]]

It was separate and unrelated test, those who believed themselves wise stepped forward.

 

[spartan231490]

Because none of them had red balls on their heads. They all see that everybody has white balls on their heads so assume that they must be the only one with a red ball.

Probably this. Either that, or they just stopped giving a shit about the balls, or they took it off thier head and looked at it.

 

[Jinjiro]

I reckon they moved forward because they knew the wise man was making a mockery of them with his riddles, so they moved forward in order to save time. Thus making them wisest of all the men there.

That or REALLY lucky guesses from the apprentices.

 

[Lullabye]

One of the more foppish ones had a hand mirror handy and passed it around or something to that affect.
Literally a ton of ways to know if you have a red ball on your head.
This is one of those "mysteries" that gets defeated by common sense.

 

[skitzo van]

They were all colorblind as hell and decided to just wing it.