zxcvboy
Level: Roachling

Rank Points: 3
Registered: 03-20-2011
IP: Logged

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!

____________________________
PUSH START TO RICH

Jatopian
Level: Smitemaster
Rank Points: 1842
Registered: 07-31-2005
IP: Logged

Clearly A. Multiple choice is for the weak.

____________________________
DROD has some really great music.
Make your pressure plates 3.0 style!
DROD architecture idea generator

Rat Man
Level: Master Delver
Rank Points: 121
Registered: 07-10-2010
IP: Logged

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?

____________________________
I'M IN SPACE!

---

[Last edited by Rat Man at 04-06-2011 05:16 PM]

Jacob
Level: Smitemaster
Rank Points: 3746
Registered: 10-01-2004
IP: Logged

It's daytime?

____________________________
New to DROD? You may want to read this.
My Holds and Levels:

Rat Man
Level: Master Delver
Rank Points: 121
Registered: 07-10-2010
IP: Logged

Dang! I thought that one was pretty hard!

____________________________
I'M IN SPACE!

zxcvboy
Level: Roachling

Rank Points: 3
Registered: 03-20-2011
IP: Logged

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?



____________________________
PUSH START TO RICH

Rat Man
Level: Master Delver
Rank Points: 121
Registered: 07-10-2010
IP: Logged

because whoever put up a portrait of the hideous Beethro got sober and took it down?

____________________________
I'M IN SPACE!

NiroZ
Level: Smitemaster
Rank Points: 1302
Registered: 02-12-2006
IP: Logged

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?

Tahnan
Level: Smitemaster

Rank Points: 2459
Registered: 11-14-2005
IP: Logged

The Guru, because he was allergic to chestnuts?

larrymurk
Level: Smitemaster

Rank Points: 1911
Registered: 12-09-2004
IP: Logged

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]

RoboBob3000
Level: Smitemaster

Rank Points: 1978
Registered: 10-23-2003
IP: Logged

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?

____________________________
http://beepsandbloops.wordpress.com/

skell
Level: Legendary Smitemaster

Rank Points: 3734
Registered: 12-28-2004
IP: Logged

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.

____________________________
My website | Facebook | Twitter

Doom
Level: Smitemaster

Rank Points: 3226
Registered: 07-05-2004
IP: Logged

skell wrote:

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

skell
Level: Legendary Smitemaster

Rank Points: 3734
Registered: 12-28-2004
IP: Logged

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 .

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

____________________________
My website | Facebook | Twitter

Jatopian
Level: Smitemaster
Rank Points: 1842
Registered: 07-31-2005
IP: Logged

So I'm assuming the monks also don't use sign language or anything?

____________________________
DROD has some really great music.
Make your pressure plates 3.0 style!
DROD architecture idea generator

Penumbra
Level: Smiter

Rank Points: 358
Registered: 02-17-2005
IP: Logged

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]

NiroZ
Level: Smitemaster
Rank Points: 1302
Registered: 02-12-2006
IP: Logged

RoboBob3000 wrote:

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

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

Yep

Thus Penumbra got it. Full explanation secreted

RoboBob3000
Level: Smitemaster

Rank Points: 1978
Registered: 10-23-2003
IP: Logged

NiroZ wrote:

RoboBob3000 wrote:

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?

____________________________
http://beepsandbloops.wordpress.com/

Penumbra
Level: Smiter

Rank Points: 358
Registered: 02-17-2005
IP: Logged

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.

RoboBob3000
Level: Smitemaster

Rank Points: 1978
Registered: 10-23-2003
IP: Logged

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.

____________________________
http://beepsandbloops.wordpress.com/

---

[Last edited by RoboBob3000 at 04-08-2011 09:29 PM]

Rabscuttle
Level: Smitemaster

Rank Points: 2460
Registered: 09-10-2004
IP: Logged

You're chasing tortoises, Achilles.

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

badabing, badaboom.

brian_s
Level: Smitemaster

Rank Points: 587
Registered: 05-27-2004
IP: Logged

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?

Maurog
Level: Smitemaster

Rank Points: 1501
Registered: 09-16-2004
IP: Logged

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.

____________________________
Slay the living! Raise the dead!
Paint the sky in crimson red!

The spitemaster
Level: Smiter
Rank Points: 354
Registered: 06-09-2005
IP: Logged

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.

____________________________
Last night upon a stair
I met a man that wasn't there
He wasn't there again today
I wish that man would stay away