• Congratulations to the Class of 2024 on your results!
    Let us know how you went here
    Got a question about your uni preferences? Ask us here

Monks. (3 Viewers)

gr_111

Member
Joined
May 2, 2012
Messages
162
Gender
Male
HSC
2012
no :\ . How can the process not occur if they all know that there is at least one blue eyed monk (or at least one brown eyed monk), and they are all as intelligent as we are assuming?

Come on, seanieg, explain...!
 

gr_111

Member
Joined
May 2, 2012
Messages
162
Gender
Male
HSC
2012
This doesn't work without being told that there is atleast 1 blue eyed monk, which can't be true since you stated there is none, so the case of having no blue eyed monks can't happen.
yeah, fine, but i was just trying to account for every different configuration.
 

seanieg89

Well-Known Member
Joined
Aug 8, 2006
Messages
2,662
Gender
Male
HSC
2007
So this is the answer I was looking for:

By telling the monks "at least one of you has blue eyes", the stranger is actually telling the monks a sequence of facts, at least one of which is new knowledge to them.

S1) At least one monk on the island has blue eyes.

S2) Every monk on the island knows S1)

S3) Every monk on the island knows S2)

Etc.

No matter how many blue eyed monks there were to begin with (excluding the trivial case of zero when the stranger is lying), at least one of these facts is new to the monks.

Eg if there were exactly two monks with blue eyes, then every monk on the island knows that there is a blue eyed monk on the island (Every monk knows S1). But the two blue eyed monks will NOT know S2 until the strangers words.
 

SunnyScience

Member
Joined
Oct 10, 2011
Messages
706
Gender
Male
HSC
2012
Is it bad that even with both solutions now, I still don't understand it? lol.
 

seanieg89

Well-Known Member
Joined
Aug 8, 2006
Messages
2,662
Gender
Male
HSC
2007
Is it bad that even with both solutions now, I still don't understand it? lol.
Not really, these things are designed to be pretty counter-intuitive. Think about it a bit and perhaps it will make more sense later.
 

barbernator

Active Member
Joined
Sep 13, 2010
Messages
1,439
Gender
Male
HSC
2012
So this is the answer I was looking for:

By telling the monks "at least one of you has blue eyes", the stranger is actually telling the monks a sequence of facts, at least one of which is new knowledge to them.

S1) At least one monk on the island has blue eyes.

S2) Every monk on the island knows S1)

S3) Every monk on the island knows S2)

Etc.

No matter how many blue eyed monks there were to begin with (excluding the trivial case of zero when the stranger is lying), at least one of these facts is new to the monks.

Eg if there were exactly two monks with blue eyes, then every monk on the island knows that there is a blue eyed monk on the island (Every monk knows S1). But the two blue eyed monks will NOT know S2 until the strangers words.
ahhh yes
 

someth1ng

Retired Nov '14
Joined
Sep 18, 2010
Messages
5,558
Location
Adelaide, Australia
Gender
Male
HSC
2012
Uni Grad
2021
I don't think this works if there is more than 1 monk with blue eyes?

If you had 1 monk with blue eyes, he'd know because there are no other blue monks (he must know).

If you had 2 monks with blue eyes, each of the blue monks will look at each other and won't be able to determine if they have blue eyes or not?
 

seanieg89

Well-Known Member
Joined
Aug 8, 2006
Messages
2,662
Gender
Male
HSC
2007
I don't think this works if there is more than 1 monk with blue eyes?

If you had 1 monk with blue eyes, he'd know because there are no other blue monks (he must know).

If you had 2 monks with blue eyes, each of the blue monks will look at each other and won't be able to determine if they have blue eyes or not?
They will see each other alive the next day and deduce that they themselves must have blue eyes. Read the earlier post on the solution in terms of induction.
 

seanieg89

Well-Known Member
Joined
Aug 8, 2006
Messages
2,662
Gender
Male
HSC
2007
Each of the three will observe that the two blue eyed monks they can see do no commit suicide on the second night. Hence all three will deduce they are blue and commit suicide on the third night.
 

someth1ng

Retired Nov '14
Joined
Sep 18, 2010
Messages
5,558
Location
Adelaide, Australia
Gender
Male
HSC
2012
Uni Grad
2021
Each of the three will observe that the two blue eyed monks they can see do no commit suicide on the second night. Hence all three will deduce they are blue and commit suicide on the third night.
So if there's three blue monks, the first one will see two but if those two don't suicide on the second night, there must be three.
That same goes if there's four blue monks? If there's no suicide on the third night, there must be four inc himself?


hmmm...interesting
 

gr_111

Member
Joined
May 2, 2012
Messages
162
Gender
Male
HSC
2012
So this is the answer I was looking for:

By telling the monks "at least one of you has blue eyes", the stranger is actually telling the monks a sequence of facts, at least one of which is new knowledge to them.

S1) At least one monk on the island has blue eyes.

S2) Every monk on the island knows S1)

S3) Every monk on the island knows S2)

Etc.

No matter how many blue eyed monks there were to begin with (excluding the trivial case of zero when the stranger is lying), at least one of these facts is new to the monks.

Eg if there were exactly two monks with blue eyes, then every monk on the island knows that there is a blue eyed monk on the island (Every monk knows S1). But the two blue eyed monks will NOT know S2 until the strangers words.
Sorry if i'm being annoying, but I still can't see how they need to know S2 for the action to start? :confused2:
 

sleepybearx

Member
Joined
Feb 21, 2012
Messages
47
Location
Sydney
Gender
Female
HSC
2014
dis is lyk s0 confuzing. who thought of this, what have you been doing with your life!?
 

Users Who Are Viewing This Thread (Users: 0, Guests: 3)

Top