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zxcvboy
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Alright, ladies and gentlemen, first question!
1. A man walked into a bar but didn't drink anything. He got hurt but he didn't get into a fight. How is this possible?

A.It was a metal bar and he tripped over it.
B.He decided to bet instead.
C.He walked in the bar, stayed for a minute, and walked out.
D.But it's impossible! He could have done one but not the other! :?

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04-06-2011 at 07:32 AM
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Jatopian
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Clearly A. Multiple choice is for the weak.

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04-06-2011 at 07:47 AM
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Rat Man
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Yeah, you made it too easy. I thought about it and got it without reading the multiple choice. My turn, though!

A man covered in black cloth from head to toe walks in front of a car. The headlights are out and there are no lights on anywhere. There are clouds in the sky and the stars and moon cannot be seen. But the woman driving the car sees him and hits the breaks. How is this possible?

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[Last edited by Rat Man at 04-06-2011 05:16 PM]
04-06-2011 at 05:15 PM
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Jacob
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It's daytime?

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04-06-2011 at 05:30 PM
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Rat Man
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Dang! I thought that one was pretty hard!

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04-06-2011 at 05:46 PM
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zxcvboy
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3. Beethro looked at a portrait. He saw his face on the frame for a minute, walked out and went in again. This time, he couldn't see it. Why?



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04-06-2011 at 09:58 PM
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Rat Man
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because whoever put up a portrait of the hideous Beethro got sober and took it down?

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04-06-2011 at 10:03 PM
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NiroZ
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quote:
zxcvboy wrote:
3. Beethro looked at a portrait. He saw his face on the frame for a minute, walked out and went in again. This time, he couldn't see it. Why?



The problem with riddles like this is that there are almost infinite correct answers, like Rat Mans. Beethro could have also not looked in that direction, or left to buy it, ect.

Try this one:

Imagine a monastery in which ten of the monks may have a disease which causes them to have blue spots on their foreheads but has no other symptoms. All the monks have taken a vow of silence, they meet just once a day, and there are no mirrors in the monastery, so nobody knows whether he has a blue spot on his forehead or not.

If a monk discovers that he has a blue spot on his forehead, he will have to leave the monastery by the end of the day. All the monks are perfect logicians – that is, they can instantly infer all the logical consequences of any statement made to them – and they all know that all the other monks are perfect logicians.

One day, the Guru, who is known to be truthful, gathers all the monks together and announces “At least one monk in this monastery has a blue spot on his forehead.” Nothing happens for nine days, but on the tenth day, all the monks with blue spots leave.

How many monks left and why?

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04-07-2011 at 06:27 AM
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Tahnan
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The Guru, because he was allergic to chestnuts?
04-07-2011 at 08:06 AM
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larrymurk
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I like the puzzle NiroZ, but I've already heard it so will leave it for others to figure out.

It seems similar to this puzzle-

3 philosophers fall asleep under a tree. A fool happens by and draws X marks on all of their foreheads. When they awaken they all start laughing then they stop. Why?

Minor hints-
One can assume a philosopher would not laugh if he knew there was a mark on his head.
One can assume all the philosophers are intelligent, reasoning people.
There is no silly trick, this can be solved by logic/reasoning.

[Last edited by larrymurk at 04-07-2011 06:36 PM]
04-07-2011 at 06:27 PM
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RoboBob3000
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quote:
NiroZ wrote:
All the monks are perfect logicians – that is, they can instantly infer all the logical consequences of any statement made to them – and they all know that all the other monks are perfect logicians.
Do all the monks know that all the other monks know that all the other monks are perfect logicians?

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04-07-2011 at 07:49 PM
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skell
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quote:
NiroZ wrote:
One day, the Guru, who is known to be truthful, gathers all the monks together and announces “At least one monk in this monastery has a blue spot on his forehead.” Nothing happens for nine days, but on the tenth day, all the monks with blue spots leave.

How many monks left and why?


Sounds like Smullyan!
I'd say there was only one monk with blue spots. He knew that there was supposed to be one man with spots, but since, during a meeting, he saw no one who had them, he deducted that it must be him.
I never was good with the riddles involving sets in Smullyan's books, I will have to properly go through them one day.

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04-07-2011 at 07:59 PM
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Doom
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quote:
skell wrote:
quote:
NiroZ wrote:
One day, the Guru, who is known to be truthful, gathers all the monks together and announces “At least one monk in this monastery has a blue spot on his forehead.” Nothing happens for nine days, but on the tenth day, all the monks with blue spots leave.

How many monks left and why?


Sounds like Smullyan!
I'd say there was only one monk with blue spots. He knew that there was supposed to be one man with spots, but since, during a meeting, he saw no one who had them, he deducted that it must be him.
In that case the monk would leave on the first day. Not the 10th. More likely

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04-07-2011 at 09:07 PM
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skell
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Doom wrote:
In that case the monk would leave on the first day. Not the 10th. More likely

He hadn't had a chance to see all the monks in the first 9 days, and only on the tenth he had seen them all, seeing that none had blue spots :P.

But honestly I don't know right now. I might get enlightened later though.

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04-07-2011 at 09:22 PM
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Jatopian
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So I'm assuming the monks also don't use sign language or anything?

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04-07-2011 at 10:41 PM
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Penumbra
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quote:
NiroZ wrote:
How many monks left and why?


If there were only one monk with a spot on his head, he would have left on the first day. This is because he would have seen that every other monk had no spots, and since at least one monk has a spot, it must be him. Therefore, he would leave.

Since no monks left the first day, all monks must have seen at least one other spotted monk. If two monks had spots, then each monk with a spot would see that the other had not left the previous day, which means the other monk must have seen another spot. Since both monks in question see only one other spot, that means they themselves have a spot, and must leave.

In this puzzle, they left on the 10th day, so I would say that all 10 of the potentially diseased monks had spots, and left.

Another way to explain it: Each spotted monk sees nine spots. Those monks are all waiting for the 9th day to see if the others leave. The rest of monks see 10 spots, and are waiting for the 10th day. Since the nine other monks do not leave on the 9th day, they all leave on the 10th. This lets the rest of the monks off the hook.


[Last edited by Penumbra at 04-08-2011 12:09 AM]
04-07-2011 at 11:59 PM
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NiroZ
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quote:
RoboBob3000 wrote:
quote:
NiroZ wrote:
All the monks are perfect logicians – that is, they can instantly infer all the logical consequences of any statement made to them – and they all know that all the other monks are perfect logicians.
Do all the monks know that all the other monks know that all the other monks are perfect logicians?

Yep
quote:
Jatopian wrote:
So I'm assuming the monks also don't use sign language or anything?

Yep

Thus Penumbra got it. Full explanation secreted

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04-08-2011 at 02:47 AM
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RoboBob3000
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quote:
NiroZ wrote:
quote:
RoboBob3000 wrote:
quote:
NiroZ wrote:
All the monks are perfect logicians – that is, they can instantly infer all the logical consequences of any statement made to them – and they all know that all the other monks are perfect logicians.
Do all the monks know that all the other monks know that all the other monks are perfect logicians?

Yep

Do all the monks know that all the other monks know that all the other monks know that all the other monks are perfect logicians?

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04-08-2011 at 04:14 PM
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Penumbra
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RoboBob3000 wrote:
Do all the monks know that all the other monks know that all the other monks know that all the other monks are perfect logicians?


At this point, I think we should just leave it up to the perfect logician monks to figure out.
04-08-2011 at 08:26 PM
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RoboBob3000
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My perfect logician monks realize that there's an infinite chain of "knowledge of knowledge" requirements before anybody can be truly certain of what everyone else knows. So each monk knows that they cannot rely on their own knowledge of other monks' knowledge. Thus, though monks do expect other monks to be perfect logicians, they do not expect them to be perfect players of this game due to their insufficient information.

If only one monk were to have a blue dot on their head, they would leave after the first day, but only that monk with the dot on their head would know that they themselves would leave in that situation. Because each monk can't expect other monks to behave optimally in this situation, we can't iterate to the two-dot mark and beyond and expect any monks to ever leave. Because no monks left on day one, that meant that every monk knew that they wouldn't ever leave unless more information entered their system.

On day ten, that must have happened. Perhaps the Guru took pity on them, realizing they didn't have enough information to self-diagnose. He probably went around and told each monk with a blue dot that they had a blue dot. Anywhere from two to ten monks went home that night.

TL;DR: There is not enough information. Anywhere from between two and ten monks left on the tenth day after an unknown source added more information to the system.

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[Last edited by RoboBob3000 at 04-08-2011 09:29 PM]
04-08-2011 at 09:27 PM
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You're chasing tortoises, Achilles.

Axioms:
* Everyone knows the axioms
* Monks are perfect logicians

badabing, badaboom.

04-09-2011 at 07:41 AM
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brian_s
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I get the point that RoboBob is trying to make. That in order for the solution to work there are a number of assumptions that must be made: all the monks think the same, they all make decisions at the same rate, etc.

Somewhere else on the web I saw a part 2 for this puzzle:
Same scenario as the original except with a few alterations: All but one of the monks is perfect and timely in their deductions and the last monk is slower than the rest. What happens if the slow monk is one of the ten with the mark, and he does not figure things out until one day later?
04-09-2011 at 04:38 PM
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Maurog
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Nothing, nothing would happen. On day 10 nine monks leave and all the perfect ones that are left stare at the slow one with the blue dot, because they know they can't be ones with the dot as per the nine perfect monks who left on day 10 clearly indicating there are only 10 dots total, not 11 as the slow monk's behavior might suggest.

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04-09-2011 at 07:18 PM
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The spitemaster
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See you all don't get the last trick. Obviously, the disease is communicable, otherwise they wouldn't be expected to leave. Thus if I was one of the monks I would leave on the first day because I don't want to get the disease while everyone else was figuring out if they had it or not.

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04-10-2011 at 12:30 AM
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