Logical puzzles

[cyclops]

puzzle.jpg (25.59 KiB) Viewed 20044 times

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

[robinz]

Can't be bothered to try to draw one and upload it, but it'll be the number 6, glued to its reflection about a vertical axis.

I saw this instantly - but that doesn't necessarily mean that I would always have done so. In any case, it's more of a visual puzzle than a logical one, surely?

[Gresil]

Something like 6d. About twenty seconds.

[cyclops]

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

[cyclops]

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 )

[Redundant]

Fuses

If I know which fuse is which, light the 10 minute fuse on both sides, and when it finishes burning in five minutes, light the 15 minute fuse.

If I don't know which is which ... not sure if it's solvable. Will have to think some more.

[Bill Spight]

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

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.

[Koroviev]

Fuses:

Light the 10 minute fuse from both ends with one match - it will burn for five minutes.

When it burns out, light the 15 minute fuse with the other match. When it burns out 20 minutes have passed.

How's that?

[hyperpape]

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?

[amnal]

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?

Cover up the left half of each symbol

[SoDesuNe]

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?

Cover up the left half of each symbol

hyperpape, I'm with you.

[hyperpape]

@amnal

Thanks. I kept looking at how 3 looked a bit like you'd fused copies of 2, then started imagining that there could be some sort of complicated pattern.

[cyclops]

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?

[Dusk Eagle]

All the people with red spots have left the island. If everyone on the island knows that their spot is either red or black, then everyone will have left by a year later. Why? See: http://xkcd.com/blue_eyes.html and http://xkcd.com/solution.html. This is basically my favorite logic puzzle of them all. Unfortunately, no one I've ever told this puzzle to is able to understand the solution.

[Monadology]

Unfortunately, no one I've ever told this puzzle to is able to understand the solution.

Really? It was used in an informal logic class I had full of a decent range of folks, and they all got it eventually.

For anyone interested, I recently read an essay by Jacques Lacan on it. It can be found here: http://www.soundandsignifier.com/files/ ... l_Time.pdf though I don't know if it's the same translation I read. Lacan is kind of pretentious, but fortunately it's not one of his obscurantist pieces. I think Lacan arguably misses the point (though I think he may also be somewhat aware of that) inasmuch as he analyses the solution as if the 'prisoners' or 'islanders' are not absolutely and equally perfect reasoners who would be acting synchronously. In any case, I think he misses the point in an interesting way.