Seen a lot of riddle threads (people post riddles, other people try to figure them out) here and there, they're great. Was thinking about it and as a coincidence, I just ran into the hardest riddle on the face of the earth, (courtesy of [ur=http://xkcd.com/blue_eyes.htmll]xkcd[/url]) so let's kick it off, see if you guys can do it. Also, feel free to post your own, have at it!

Blue Eyes:
The Hardest Logic Puzzle in the World[/center][/b]

A group of people with assorted eye colors live on an island. They are all perfect logicians -- if a conclusion can be logically deduced, they will do it instantly. No one knows the color of their eyes. Every night at midnight, a ferry stops at the island. If anyone has figured out the color of their own eyes, they [must] leave the island that midnight. Everyone can see everyone else at all times and keeps a count of the number of people they see with each eye color (excluding themselves), but they cannot otherwise communicate. Everyone on the island knows all the rules in this paragraph.

On this island there are 100 blue-eyed people, 100 brown-eyed people, and the Guru (she happens to have green eyes). So any given blue-eyed person can see 100 people with brown eyes and 99 people with blue eyes (and one with green), but that does not tell him his own eye color; as far as he knows the totals could be 101 brown and 99 blue. Or 100 brown, 99 blue, and he could have red eyes.

The Guru is allowed to speak once (let's say at noon), on one day in all their endless years on the island. Standing before the islanders, she says the following:

"I can see someone who has blue eyes."

Who leaves the island, and on what night?

-----------------------------------------------------------------------------

There are no mirrors or reflecting surfaces, nothing dumb. It is not a trick question, and the answer is logical. It doesn't depend on tricky wording or anyone lying or guessing, and it doesn't involve people doing something silly like creating a sign language or doing genetics. The Guru is not making eye contact with anyone in particular; she's simply saying "I count at least one blue-eyed person on this island who isn't me."

And lastly, the answer is not "no one leaves."


don't post the answer if you already know it ok :)​))

Wouldn't any/all of the blue-eyed people leave after counting 200 people on the island without the guru, counting 100 brown-eyed people and 99 blue-eyed people, and assuming that there is an equal amount blue-eyed and brown-eyed people then assuming that they are the missing blue-eyed person? Maybe they all get to leave since they are all perfect logicians.

I still can't figure out what would change after the Guru speaks. Statistically, nothing. I just don't understand how it can change anything because she is merely confirming someone has blue eyes, a fact which everyone on the island already knows.

This. She's just confirming what everyone knows, I don't know how she's changing anything.

http://xkcd.com/solution.html

I read the solution, and it doesn't make a whole lot of sense to me.  I can kind of see where it's going, but it's not one of those "aha!" kind of riddles.  It's more like an "Oh... whatever."

Took me awhile to wrap my head around this one, but I think I got it.


So am I right?  I'm not going to check the solution just in case I am not in fact correct.

Summoner, yes that's the one!

awesome.  I feel smart now.

Its odd. The guru to me seems like a red herring, but if he indeed was one, the problem would no longer make sense: If they are all perfect logicians, you must logically conclude that the guru will use his only communication to the others in a meaningful and important way, and bend your mind all around his revelation. You must also conclude that the other island dwellers will also take into account the fact the guru SHOULD be saying something meaningful. I CALL BULLSHIT MUHUHU.

(in my opinion, if its the case, which sounds very likely, the guru was added by someone else who thought the problem could use some complication, not realizing that he is in fact harming the riddle and not making it better.)

Ill try like, making some hypothetical situations and ill prolly end up getting the solution, you just wait!

I almost fell in the same pit-trap as NinjaPirate at first, but I drew some nice pictures, talked to myself for fifteen minutes, re-read the question and the rules (this is where I got out of the loop) and after that I got it right. Great rush!

Anyone got some more nasty ones on top of their heads?

The batman movie had fantastic riddles!! here is my favourite

Commissioner Gordon: What weighs six ounces, sits in a tree and is very dangerous?
Robin: A sparrow with a machine gun!
Commissioner Gordon: Yes, of course

 :incred:

This is from Yahoo! Answers.

Best riddle:
"What have I got in my pocket?"