This riddle has me stumped.

[ih8thisname]

Daughter emailed me this yesterday and having passed it around work all day in search of an answer (to no avail) I present it to the wisdom of PH. So here goes;

On a remote island lives a happy tribe. The island is so small that everybody knows everybody. The inhabitants are extremely intelligent and rational, except for the following: It is considered to be a big shame to have blue eyes. If one inhabitant discovers having blue eyes, he/she will flee from the island at midnight and never come back. Luckily there are no mirrors on the island, nobody knows genetics and everybody is too polite to talk about anybody's colours of eyes. One day a missionary comes to the island. As he is about to leave he tells everybody that he finds it strange that there are two colours of eyes in such a small community, blue and brown. On the 43rd night after this happens, many inhabitants flee from the island.

How many persons were blue-eyed on the island? (Hint: use induction on the number of blue-eyed inhabitants.)

[paul.deitch]

answers to this are in the internet, including wiki

[baptistsan]

None. They'd all left?

[Rouleur]

42

[Gixer86]

42??

[mullerrice18]

1

[Mulder]

I'm going with 1 as well.

[E21_Ross]

it's flawed....

it could be just 1. if nobody knows themselves whether they have blue eyes, and all are too polite to tell other people, they may all begin to think they may have blue eyes, and so flee the island. but it could also be all of them?

but then...why the 43rd day?

can it actually be answered?

[dibbly dobbler]

I cheated - it can be worked out though, no trick required.

[TheEnd]

i think it's 43, the reason being they all sit around, and after 42 days, no one has ran away, primarily due to them not realising they have blue eyes, and on day 43, they assume they must be the blue eyed person, and make tracks.

although i still think that's full of logic holes

[CaptainSlow]

should be 43

[ih8thisname]

It might be worth pointing out that it was in fact my daughter who sent me this... The same one who believed for 17 years that there was a fence that ran across the bredth of the country separating Scotland & England...

[E21_Ross]

the answer is possibly 1.

nobody thinks they have blue eyes. every night, 1 person tells one other person that someone has blue eyes. it takes 43 days to circulate round the island (1 person per night). everyone too polite to say who has blue eyes, and nobody has left on 43rd day, so they think it's them.

no?

either that or 42, 43 or 44?

Edited by E21_Ross on Thursday 29th April 19:29

[Curry Burns]

ih8thisname said:

It might be worth pointing out that it was in fact my daughter who sent me this... The same one who believed for 17 years that there was a fence that ran across the bredth of the country separating Scotland & England...

Oh dear.......

[TheEnd]

ih8thisname said:

It might be worth pointing out that it was in fact my daughter who sent me this... The same one who believed for 17 years that there was a fence that ran across the bredth of the country separating Scotland & England...

you mean Hadrian's fence?

[dibbly dobbler]

spoiler - solution for a very similar riddle

[K87]

E21_Ross said:

it's flawed....

it could be just 1. if nobody knows themselves whether they have blue eyes, and all are too polite to tell other people, they may all begin to think they may have blue eyes, and so flee the island. but it could also be all of them?

but then...why the 43rd day?

can it actually be answered?

But he told everyone, so it wouldn't have taken 43 days to circulate.

[K87]

That solution makes sense. Pretty obvious really when you see it, dont see how it took the guy who wrote the solution so long to believe it after he found out.

[E21_Ross]

K87 said:

E21_Ross said:

it's flawed....

it could be just 1. if nobody knows themselves whether they have blue eyes, and all are too polite to tell other people, they may all begin to think they may have blue eyes, and so flee the island. but it could also be all of them?

but then...why the 43rd day?

can it actually be answered?

But he told everyone, so it wouldn't have taken 43 days to circulate.

doesn't say he told them all at once though....?

[E21_Ross]

K87 said:

That solution makes sense. Pretty obvious really when you see it, dont see how it took the guy who wrote the solution so long to believe it after he found out.

the only thing is though....under those circumstances where people won't tell you if you're eyes are blue, you may get people leaving, even if their eyes aren't blue, if blue-eyed people don't leave, then said non-blue-eyed person would leave, thinking they have blue eyes?

no?