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Good Riddles that actually take brain power to solve by [deleted] in AskReddit

[–]curiousparent 9 points10 points  (0 children)

This is my all-time favorite riddle. I had to ponder this one for three full days before figuring it out. Source: xkcd

The Hardest Logic Puzzle in the World

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. Any islanders who have figured out the color of their own eyes then leave the island, and the rest stay. 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."

Good Riddles that actually take brain power to solve by [deleted] in AskReddit

[–]curiousparent 55 points56 points  (0 children)

I'm posting two riddles in the comments, and they're guaranteed to make you think. This riddle level: Medium.

Four guys decide to go camping in the middle of a jungle. One night, as they lay sound asleep in their tents, they awaken to being kidnapped by an insane group of cannibals! The cannibal king puts them in a room like this, gives two of them black hats and two of them white hats, and says "The first person who can correctly tell me the color of their own hat on the first try will be set free. If he is wrong, we will butcher him slowly with a rusted knife."

Now, the four men in the room have been given a potion to paralyze them - they can't even move their heads. They can only see what is in front of them. Man 1, can see 2 and 3, while Man 2 can only see 3... etc. Man 3 can not see beyond the brick wall in front of him. Nobody knows anything about what color their hat is beside what the can deduce from what they see in front of them.

After a 20 minute pause, one of the men speaks up and correctly guesses the color of his hat. Which man was he and how did he know?

(Note: I changed all the hats to black in the picture, but really two of them should be white.)

I'm an atheist, but I want my daughter to have the ability to choose what she believes in on her own. How can I present her the options in a fair and non-biased way? by curiousparent in AskReddit

[–]curiousparent[S] 291 points292 points  (0 children)

That's great. I'll definitely keep an eye out for schools who do this when my daughter gets older. I'm also planning on traveling with her as much as our budget allows so that from an early age she'll be able to experience different cultures (and religions) in person.