Author |
Topic: FORK IN THE ROAD I (Read 19724 times) |
|
arvind mayank
Guest
|
the answer is he gone ask both the question that ---
from which direction are u from.
the person from city of safety will point in the direction of the city of safety and person from cannibals bcoz he has lie will too point at the direction of the city of safety.
bingo bcoz boths persons answer are same and one of them always tell the truth the direction point to none aother to the city of safety
|
| « Last Edit: Sep 1st, 2003, 7:30pm by Icarus » |
 IP Logged |
|
|
|
Chronos
Full Member
Gender: 
Posts: 288
|
 |
Re: FORK IN THE ROAD I
« Reply #1 on: Oct 14th, 2002, 6:57pm » |
 Quote  Modify
|
It occurs to me that "Which direction are you from" is not, in fact, adequate. If you ask it of the truth-teller, of course, you're fine. But if you ask the liar, he doesn't have to point to the city of truth. The only requirement is that he point to someplace other than his home town. So he might, for instance, point straight up, or back in the direction you came from, and still be lying. You'd then know that he was the liar, but you'd still need another question to get the answer from the truth-teller.
You need to phrase your question in such a way that there are only two valid answers.
|
|
IP Logged |
|
|
|
arvind mayank
Guest
|
there are only three way to go(i have to decide from two directions only) and if he is pointing in my direction i get to know he is lying and other person is telling the truth
|
|
IP Logged |
|
|
|
Chronos
Full Member
Gender:
Posts: 288
|
|
Re: FORK IN THE ROAD I
« Reply #3 on: Oct 21st, 2002, 11:01pm » |
Quote Modify
|
There are only three directions to go, but there are an infinite number of directions he can point. And you're only allowed one question, so if all you learn is that he's the liar, then you're stuck.
|
|
IP Logged |
|
|
|
Eric S
Guest
|
You simply ask one of them:
"What will the other guy tell me if I ask him if this path goes to the city of safety"
If you are pointing to the City of Safety:
1) You talk to the Truth Teller, he will say No because he knows the other guy will lie and say No.
2) You talk to the Liar, he will say No because he knows the other guy will say Yes, but he is a liar so he will lie about that and say No.
If you are pointing to the City of Cannibals
1) You talk to the truth teller, he will say Yes because he knows the other guy will lie and say Yes this is the City of Safety
2) You talk to the liar, he will say Yes because he knows the other guy will say No this is not the path to the city of safety, so he has to lie and say Yes.
So if you talk to one of them and they say "The other guy will say No if you ask him if this route goes to City of Safety", that is the route to the City of Safety.
|
|
IP Logged |
|
|
|
Eric S
Guest
|
And yes, this solution works for Fork in the Road II I believe.
The difference between the problems is the brothers aren't from the villiage.. they are just sitting there.
With the Fork in the Road I, the guys are from the villiages, so it makes it a bit easier.
|
|
IP Logged |
|
|
|
mal
Guest
|
i have one
ask one of them "what is my name?"
you know the right answer to that
and if you end up asking the honest one then they will say your name of course
if you ask the liar then they will tell you another name than your own
|
|
IP Logged |
|
|
|
Chronos
Full Member
Gender:
Posts: 288
|
|
Re: FORK IN THE ROAD I
« Reply #8 on: Nov 9th, 2002, 1:30pm » |
Quote Modify
|
OK, so the answer you get is "Your name is Bob". Which direction do you go?
You're only allowed to ask one question, so finding out who's who isn't enough.
|
|
IP Logged |
|
|
|
mal
Guest
|
um.. yeah you totally missed my answer...
my name is mal and when i ask that question i expect that is what thier answer should be... geeeet it?
i am asking them what MY name is... NOT THIER NAME
|
|
IP Logged |
|
|
|
towr
wu::riddles Moderator
Uberpuzzler
Some people are average, some are just mean.
Gender:
Posts: 13730
|
|
Re: FORK IN THE ROAD I
« Reply #10 on: Nov 14th, 2002, 1:29am » |
Quote Modify
|
And with that you know who tells the truth, but you can't ask him where you should go since you wasted your only question..
You don't need to know who tells the truth, you need to know which way you should travel..
|
|
IP Logged |
Wikipedia, Google, Mathworld, Integer sequence DB
|
|
|
James Fingas
Uberpuzzler
Gender:
Posts: 949
|
|
Re: FORK IN THE ROAD I
« Reply #11 on: Nov 14th, 2002, 7:57am » |
Quote Modify
|
In fact, here is a more general statement about what you can learn:
1) Since you only ask one yes/no question, you only get one bit of information.
2) Learning which road to take requires one bit of information
3) Learning which person is which requires one additional bit of information.
4) Based on this, if you learn which road to take, then you cannot learn which person is which. If you learn which person is which, you can't learn which road to take.
So one common thread of all correct answers is that they don't reveal who is who.
|
|
IP Logged |
Doc, I'm addicted to advice! What should I do?
|
|
|
just some random guy
Guest
|
if i remeber right the answer was that both of them could not be trusted because they were both liars....or maybe that was the answer to one of the other forks in the road?
|
|
IP Logged |
|
|
|
george bush
Guest
|
The way that works, without having to use braincells to come up with a specifically useful question is to yell "Free Beer at The City of Safety", and then just follow them
|
|
IP Logged |
|
|
|
riddle solving fool
Guest
|
Here is a question that will satisfy both of the Fork in the Road riddles:
Say to either of them, "Which road would you tell me is the way to the City TOMORROW?"
If the truth teller was asked, he would tell you the right road because he always tells the truth
If the liar was asked, he knows he would lie and say the wrong way tomorrow, so he must lie and tell you the opposite. Therefore he says the opposite of the wrong way and shows you the right way. Double negative
Either one you ask, you get the correct way. 
|
|
IP Logged |
|
|
|
Vincent_469
Newbie
Gender: 
Posts: 21
|
|
Re: FORK IN THE ROAD I
« Reply #15 on: Jan 12th, 2003, 7:27pm » |
Quote Modify
|
What is exactly the answer to both one and two?
I think one is "show me each of your villiages" and the truth teller will point to his door and the lier will point to the truth teller and there you go...
But in # 2 I don't get it....
(In YU-GI-OH! they had something like this with the paradox brother to choose a door but Yu-Gi found out what if they're both lying and stuff...) Anyway...what's the answer to # 2? 
|
|
IP Logged |
|
|
|
redPEPPER
Full Member
Posts: 160
|
|
Re: FORK IN THE ROAD I
« Reply #16 on: Jan 13th, 2003, 7:10am » |
Quote Modify
|
Vincent:
An answer to both I and II has been provided several times in this thread, including just before your post. Did you miss it?
As for your proposition of "show me each of your villiages" (sic) there are a few problems with it.
First it's not a question 
Second, if you reformulated it as a question, you're only allowed to ask it to one of the guys, not both guys at once.
Third, if you asked it to one of the guys and it happened to be the liar, he wouldn't point towards his village but he might point anywhere else, as Chronos pointed earlier in the thread. So you'd know he's the liar but you wouldn't know where to go.
|
|
IP Logged |
|
|
|
telkwa
Guest
|
I think the 'best' solution to all the fork in the road type questions is to say "If i were to ask you <whatever>, what would you say?"
Regardless of whether or not you have two liars, one liar one truth teller, etc. - you always get the correct answer.
|
|
IP Logged |
|
|
|
towr
wu::riddles Moderator
Uberpuzzler
Some people are average, some are just mean.
Gender:
Posts: 13730
|
|
Re: FORK IN THE ROAD I
« Reply #18 on: Mar 9th, 2003, 7:29am » |
Quote Modify
|
on Mar 8th, 2003, 9:19pm, telkwa wrote:I think the 'best' solution to all the fork in the road type questions is to say "If i were to ask you <whatever>, what would you say?"
Regardless of whether or not you have two liars, one liar one truth teller, etc. - you always get the correct answer. |
|
That works if there are only two possible answer, but if you lie you can make up many more answers..
The liar could even subtely lie, and if he would normally say 'right' he could lie and say he would say 'the way to the right' or 'not left', which have the same semantics, but different form and thus isn't the same..
|
|
IP Logged |
Wikipedia, Google, Mathworld, Integer sequence DB
|
|
|
aero_guy
Senior Riddler
Gender:
Posts: 513
|
|
Re: FORK IN THE ROAD I
« Reply #19 on: Mar 9th, 2003, 1:03pm » |
Quote Modify
|
I guess you need to preface your question by making it true/false.
|
|
IP Logged |
|
|
|
goolsnut
Guest
|
What if you ask: "Which of these two paths leads to your city?"
If you ask the truth teller, he'll point you to the good city.
If you ask the liar, he'll point you to the good city as well, since he can't point to his city.
goolsnut
|
|
IP Logged |
|
|
|
rmsgrey
Uberpuzzler
    
Gender:
Posts: 2873
|
|
Re: FORK IN THE ROAD I
« Reply #21 on: May 15th, 2003, 1:46pm » |
Quote Modify
|
And, of course, this all assumes that the guy who lies is honest about it and always answers the exact negation of the truth, and also is good enough at logic to follow your question. If he treats your question as being simply a stylised way of asking "is it that way to safety" (like the french literally ask "what is it that it is" for "what's that") then you're sunk. Similarly if his intent is not to always speak the negation of the truth, but instead to always deceive (an equally valid meaning of "lie") then whatever cunning question you concoct he can always just invert the answer his truthful colleague would give - in which case your best bet is probably the "Free Beer" option after all
|
|
IP Logged |
|
|
|
goolsnut
Guest
|
Yeah, I see your point. I realized it shortly after I posted. Ohh well.
The problem with this is that a cunning liar could always say something like "I don't know" no matter what the question is (if he knows the answer, then the response "I don't know" is a lie). In that case, you're screwed no matter what you ask.
goolsnut
|
|
IP Logged |
|
|
|
rmsgrey
Uberpuzzler
Gender:
Posts: 2873
|
|
Re: FORK IN THE ROAD I
« Reply #23 on: May 15th, 2003, 8:22pm » |
Quote Modify
|
With a deceitful liar you're completely stuck anyway - you can't even tell who's truthful and who's deceitful - since the aim is to deceive, the deceitful liar will tell the truth when asked questions to which you already know the answer (knowing he can't deceive you about the answer, he opts to deceive you about his nature)
There is usually an assumption that everyone involved (except you) knows everything (and hence is also a perfect logician) which, incidentally invalidates the "free beer" approach - unless one guy says "no there isn't", and that the liar always negates the truth - and the only answers anyone can give are yes and no.
The problem gets more interesting when you assume that the natives fail to understand any complex questions (anything involving logical connectives such as and, or, if-then). In this situation, the intended answer to Fork I still works, but I think Fork II might be impossible.
|
|
IP Logged |
|
|
|
Ryptor{GoJ}
Guest
|
I believe the answer had to be a yes or no question
|
|
IP Logged |
|
|
|
|
RIDDLES SITE
WRITE MATH!
Home 
Help 
Search 
Members 
Login 
Register
Reply
Notify of replies
Send Topic
Print
Remove