Unfork your way through...
Two tribes live in a jungle - the truth tellers (who always speak the truth) and the liars (who always lie). A traveler is walking along a path when he comes to an unmarked fork in the road. One path goes to his hometown. And he does not know which. Just then, a native comes along belonging to one of the two tribes mentioned above. What is one question he could pose to the native so that he finds his way home? (0.5 points)
posted by littlecow at 2/15/2006 07:31:00 PM
16 Comments:
i've seen this puzzle before, i abstain.
So have I . Gah.
it woan move me up the rankings, else wouldve posted.
:)
argh! i did wonder if junta would have seen this before i posted... but then... it was a good puzzle! ok, we will leave it for the new comers and move on to the next one.
Let's say the traveller comes from the town A,and the two roads lead to X (his hometown) and Y respectively.
Then,he should proceed as follows:
He mentions that he hails from his hometown X.
Then he poses the question: which of the remaining two roads leads to A?
1.Liar points at the road to Y
2.Truth teller points at the road to A
Knowing the actual route to A,the explorer can sort out his dilemma and figure out the route to his hometown (and also give the liar a piece of his mind if that may be the case!)
@sai: But the traveller is allowed only one question! So, if he has exhausted his one question in finding out whether the person he meets is a truth teller or a liar, he cannot ask them which road leads to his hometown. [as for the piece of mind, yes... yes, he can sure beat him up] ;)
Try again.
Ok,here is a second attempt:
Using nomenclature from the previous post,let the traveller point at one of the roads to X or Y and tell the tribal that he is from X.Then he indicates the other unknown road and asks the native whether it is the road to A.
If the native is truth telling,he would say "no".Thus the traveller would realise that he had pointed to the right direction of X.
If the native is a liar,he would say "yes".The traveller would realise in that case that he had pointed in the wrong direction of X,and the road he had pointed to leads to Y.
For some reason the above solution doesn't seem totally convincing to me, I'd like to know what others think.
@sai: This again would only determine whether the guy is a truth teller or a liar. The truth teller would say "no" and yet, we still dont know if it is the road to X or Y.
Ok, I will redo the puzzle....but I wiil be able to post it only next week.
Until then,goodbye and have a great week ahead!
I have no idea what this site is about I accidentally found it when trying to prove to a friend that 'unfork' is not a word. Anyway the question to ask is "What would a member of the tribe that you're not a member of tell me is the correct way home?"
If the native is a liar, he knows the other tribe would point to the correct road, so the liar would point to the wrong road as he has to lie about which road the truth teller would point to. So now the traveler knows which road is wrong and therefore can easily deduce what is right.
If the native is a truth-sayer, he knows the liar would point to the wrong road, and so truthfully points to what the liar's lie would be. Once again the traveler now knows which road is incorrect and can easily find the correct one.
@gandulf: Good job! So, basically it is a clever use of a double negation.
Do you have a url so that you can be linked from the points table?
ps: It does not look like unfork is a word, does it?
Drat....solved even before I could begin some serious work on the puzzle.But anyway, congrats to gundulf!
Thank you. I'm afraid I have no URL, nor have I figured out what these points are for. Then again haven't figured out what this site is for. Some sort of puzzle blog? Interesting concept. I might hang around. Though I'm not so good at math puzzles which seem to make up the majority of the puzzles on here.
oops forgot to sign my name.
@Gundulf: We are a group of fellows who like solving puzzles. While our focus has been on logic/math puzzles thus far, we have decided to expand out to other puzzles too. Now that you are on the points table, you could also contribute puzzles to the forum. Just put it in the comments section and if it is original/tough/innovative, we will have it on the main board.
Welcome back, once again!
If I ask you "if this road does not go to my home town" would you answer yes?
(Right road, Liar) : ans: no.
(Wrong road, Truth teller) : ans: yes
(Right road, Truth teller) : ans: no
(Wrong road, Liar) : ans: yes
Does that make sense?
Yup. That is another question that would solve the problem. Good work, Gabbar!
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