Can You Solve 'The Hardest Logic Puzzle In The World'?

ikillbears

ikillbears

ikillbears

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This is a little thing that has started over on io9. It began a few months ago where they posted this little brain teaser

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with the questiong : Can you explain the numbering system in this parking lot?

It has now evolved into a sunday teaser counting up to 100. Knowing this board is filled with all manner of nobel prize winning arm chair scientists and intellectuals ( looking at you asim ) here is the link to number 1 http://io9.com/can-you-solve-the-hardest-logic-puzzle-in-the-world-1642492269

Incase people can't access it, here it is

You visit a remote desert island inhabited by one hundred very friendly dragons, all of whom have green eyes. They haven't seen a human for many centuries and are very excited about your visit. They show you around their island and tell you all about their dragon way of life (dragons can talk, of course).

They seem to be quite normal, as far as dragons go, but then you find out something rather odd. They have a rule on the island which states that if a dragon ever finds out that he/she has green eyes, then at precisely midnight on the day of this discovery, he/she must relinquish all dragon powers and transform into a long-tailed sparrow. However, there are no mirrors on the island, and they never talk about eye color, so the dragons have been living in blissful ignorance throughout the ages.

Upon your departure, all the dragons get together to see you off, and in a tearful farewell you thank them for being such hospitable dragons. Then you decide to tell them something that they all already know (for each can see the colors of the eyes of the other dragons). You tell them all that at least one of them has green eyes. Then you leave, not thinking of the consequences (if any). Assuming that the dragons are (of course) infallibly logical, what happens?

If something interesting does happen, what exactly is the new information that you gave the dragons?
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" This is not a trick question. There's no guessing or lying or discussion by or between dragons. The answer does not involve Mendelian genetics, or sign language. The answer is logical, and the dragons are perfectly logical beings. And no, the answer is not "no dragon transforms." "

The second one is here but it does show the answer to the first : http://io9.com/can-you-solve-the-worlds-other-hardest-logic-puzzle-1645422530

lets see what every ones got :)
 
87 simple. Flip picture and count :D

they would all turn into sparrows. They would all be paranoid of being green eyed and ask each other.

Last one there's thousands of gods so where do I even begin :confused:.

Edit: lol completely misread the God question :D
 
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Ouch I almost literally face palmed when I worked out the numbering system :S

this one literally had me standing on my head trying to solve it

The green eye dragon one is a bit weak IMO even with infallible logic theres the possibility of more than 1 sound line of reasoning.

Can't get my head around the gods one tonight but guessing its a variants of the old 3 suspects logic puzzle.
 
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1) Each dragon can see that every other dragon has green eyes

2) The person tells the dragons that atleast one of them has green eyes

3) The dragons already know this, infact, logically each dragon knows that atleast 99 of them has green eyes.

4) Midnight nothing happens

5) Next day every dragon, realizes that he must also have green eyes, that midnight they turn all into sparrows.

However even that is BS, the correct answer is that it is that it is a paradox, they already know what you told them, thus you cannot tell them because they would all be sparrows
 
the dragon one is really simple, it's not really a paradox.... simply nothing would change from the norm before the human visited.

The dragon needs to find out if they have green eyes, the human didn't say which one had green eyes, just that at least one does, they already knew this.

Individually they still don't know if they have green eyes and seeing as they don't talk about it or have mirrors they would not find out about their eye colour unless they changed those 'rules' about discussing it - therefore they would remain blissfully ignorant to their own eye colour. Logic would dictate that they have to have proof of their own eye colour before taking action...they have no way of getting this now the human is gone. :)

You could also have said they're all colour blind (green end of the spectrum) so don't know what green is :)

edit: how did they logically come up with the 100th day they all turn into sparrows.... their answer is not logical in the slightest
 
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Diagro said:
The dragons would change on the 100th day. The end
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This is correct. But you need to explain why - and why someone saying it out loud is critical to the chain reaction that would cause everyone to change on the 100th day.

So, if all except one dragon had blue eyes, that one greed eyed dragon would see that 99 of his friends had blue eyes, and he would know he was the one and would have to change.

So, what if two had green eyes? Well, each green-eyed dragon would know there was at least one green-eyed dragon - the one he can see. Knowing that dragons logic to be infalible, he would also know that the other would change into a sparrow after the first night, if the first rule was true. He doesn't, therefore, you know that he can also see a green eyed dragon. Which must be you, because you can see there are no others. Both green eyed dragons would work this out, and thus both change on the second night.

This same logic applies for any number of dragons, which is why on the 100th day, they all realise that no one else has changed, thus each one realises they too must have green eyes. And the human just committed genocide. As usual.

The key to the human telling them all something they already know, is it gives a hard reset point at which the chain reaction can start... not really sure how better to phrase this. But without this, they can't know that every other dragon is waiting for the green-eyed ones to turn into sparrows.
 
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MadFruit said:
This is correct. But you need to explain why - and why someone saying it out loud is critical to the chain reaction that would cause everyone to change on the 100th day.

So, if all except one dragon had blue eyes, that one greed eyed dragon would see that 99 of his friends had blue eyes, and he would know he was the one and would have to change.

So, what if two had green eyes? Well, each green-eyed dragon would know there was at least one green-eyed dragon - the one he can see. Knowing that dragons logic to be infalible, he would also know that the other would change into a sparrow after the first night, if the first rule was true. He doesn't, therefore, you know that he can also see a green eyed dragon. Which must be you, because you can see there are no others. Both green eyed dragons would work this out, and thus both change on the second night.

This same logic applies for any number of dragons, which is why on the 100th day, they all realise that no one else has changed, thus each one realises they too must have green eyes. And the human just committed genocide. As usual.

The key to the human telling them all something they already know, is it gives a hard reset point at which the chain reaction can start... not really sure how better to phrase this. But without this, they can't know that every other dragon is waiting for the green-eyed ones to turn into sparrows.
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I don't see how that logic applies to more than three dragons. If a green eyed dragon can see 3 more green eyed dragons, the he knows each of those dragons can see another 2 dragons with green eyes (plus himself, but he doesn't know that), so no-one will be able to be sure that they themselves have green eyes.

I believe it's that a dragon can see everyone has the same colour eyes, so if at least one has green, then either the individual must be the only one, or everyone else has green eyes. If the others don't change on the first day, and they won't due to not being sure of their own eyes, each individual assumes they must be the one with green eyes or they all must.
 
I think I get the 100 day logic. As the days pass the number of confirmed dragons with green eyes increases until on the 100th day that number includes the whole population, following MadFruits logic.

Every dragon can only be sure they have green eyes after the 99 other dragons confirm it for them, by still being dragons after 99 days as they can still see a 100th, you.
 
cheesyboy said:
I don't see how that logic applies to more than three dragons. If a green eyed dragon can see 3 more green eyed dragons, the he knows each of those dragons can see another 2 dragons with green eyes (plus himself, but he doesn't know that), so no-one will be able to be sure that they themselves have green eyes.
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Part of the solution is that you know all the other dragons also have perfect logic. If you can see three dragons and after the third night they do not turn into sparrows, then you too must have green eyes... because they can all see three green eyed dragons too.

It's a simple case of... how many dragons can I see with green eyes. If after N nights they do not turn into sparrows, then I also have green eyes.

A dragon who can see no green eyes, knows he is the one with green eyes, as there has to be one. Thus he will turn into a sparrow on the first night.

A dragon who can see one pair of green eyes knows that if that dragon does not turn into a sparrow on that first night, then he too can see a pair of green eyes. Thus I must have green eyes, and we both turn on the second night.

A dragon who can see two pairs of green eyes knows that if those dragons do not turn into sparrows on the second night, then I too must have green eyes and must turn into a sparrow on the third night.

A dragon who can see three pairs of green eyes knows that if those dragons to not turn into sparrows on the third night, then I too must have green eyes and must turn into a sparrow on the fourth night. Four dragons, four nights.

It just keeps going on upto any number you fancy. The logic doesn't change.
 
MadFruit said:
It is really simple... but you got it wrong :p
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as I said the answer on the site is not logical, it's all assumption based, therefore it can't be right :rolleyes:

and you're missing a fine detail, the same as the original site did. They have to find out that the individual dragon has green eyes, a very specific detail. The human did not say ALL of them have green eyes therefore by logic it means that 1 or more may not have green eyes. Because logic is based on facts rather than theories they would never be able to confirm said details about their own eyes because like I said they don't talk about it and they have no mirrors (they clearly ignored water/glass etc....). They've known for ages that 99 others have green eyes but nothing has happened because no one has told the others they specifically have green eyes meaning each dragon does not know that they have green eyes and must give up being a dragon.

If and I mean if the dragons took a leap of faith, which they wouldn't do as they're logical, then they could change on the first night. The logic would be that statistically speaking if 99 out 100 have green eyes then the odds are that all of them have green eyes and they'd all change on the first night. However they wouldn't do this because of the facts presented to them.

But then there is one side of the argument that everyone ignores...logically none of them would want to become a sparrow and give up their dragon 'powers'. They have to relinquish the power, it's not taken from them, meaning they have to give it up IF they ever find out they have green eyes, so by adding in the original rules this would never happen, even with the human comment. They would be doing everything they can not to find out.
 
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