Describe the next figure in this array. How long did it take you?

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I think I am so I think I am.

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So you've got an eye?
That don't impress me much

congratulations both. Both very fast. Easy for go players???

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I think I am so I think I am.

Next puzzle:
You have 2 lenghts of fuse and 2 matches. One fuse will burn from start to end in 10 minutes. The other in 15 minutes. However the burn rate is not steady along their lenghts. Measure 20 minutes of time.

( for the not native english: a fuse is the sort of rope they used to ignite bombs in the good old days, also used in fireworks. It has nothing to do with electricity OC )

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I think I am so I think I am.

Fuses

Who knows? It might be hard for go players. After all, solving it demands breaking down the gestalts. That might be difficult for a whole board thinker.

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Sheik Yerbuti -- if that really is your name --

Fuses:

I'm dumb enough not to get the first one, and have suppressed my shame enough to admit it. Even after reading the answers, I can't see why it would be that way. Explanation?

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When you think your opponent has made a mistake, that's when you should be the most cautious.

hyperpape, I'm with you.

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My "guide" to become stronger in Go

@amnal

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When you think your opponent has made a mistake, that's when you should be the most cautious.

Both answers correct for the fuses problem. Next problem.

on a strange island there lives a strange tribe of 300 perfectly logical and perfectly intelligent persons. And they know it of each other. Each member has a spot, red or black, on the back of the head. Nobody knows the color of his own spot but they do know the color of everybody else's. If a tribesman ever realizes the color of his own spot it is strict custom that he publicly announces this fact the next morning and leaves the island forever. So they never mention spot colors and have no mirrors. But one day a tourist, American OC, visits the island and announces to the entire tribe: "I can see at least one of you has a red spot!". The tourist leaves to return a year later.
He is surprised. Why?

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I think I am so I think I am.

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Memories of a sorceress girl
Endless fascination with the secrets of the world

I'm going to say that one's not the hardest.

Here's a harder one that originated with Raymond Smullyan:

Three gods A, B, and C are called, in some order, True, False, and Random. True always speaks truly, False always speaks falsely, but whether Random speaks truly or falsely is a completely random matter. Your task is to determine the identities of A, B, and C by asking three yes-no questions; each question must be put to exactly one god. The gods understand English, but will answer all questions in their own language, in which the words for yes and no are 'da' and 'ja', in some order. You do not know which word means which.

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When you think your opponent has made a mistake, that's when you should be the most cautious.

Haven't worked out a total solution yet, but I have figured out how to make Truth's head blow up:


EDIT: that's not necessarily a full solution for Truth either - if False is a literal-minded negative answerer, he may also have issues answering. My guess as to his answer depends on him being somewhat of a trickster and also somewhat antipathic toward Truth (and therefore might answer firmly but misleadingly rather than striking you with lightning ambiguously.)

Wonderful puzzle. I could not solve it but at least understand the solution

Here is my favourite one:

There are 10 boxes full of golden coins. 9 of the boxes contain 100 gram coins, and one of them 110 gram coins. You are allowed to weigh only once for finding out which one of the boxes contains the 110 gram coins.
(Note: By weighing I mean not comparing two (sets of) coins with each other but really measuring how many grams a (set of) coin(s) weighs.).

If you hear it for the first time it may not be so simple to solve. But once you know the solution it seems very very obvious, which is for me a good indication of a quality puzzle.

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If you say no, Elwood and I will come here for breakfast, lunch, and dinner every day of the week.

Weighing:

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So you've got an eye?
That don't impress me much

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If you say no, Elwood and I will come here for breakfast, lunch, and dinner every day of the week.