[wolfgang]

There are three men,a truth teller( always tells the truth),a YES answerer(always answers with yes),and a NO answerer(always answers with no).Each man knows who is who.

Your aim is to find who is who by asking only three YES or NO questions.

Each question should be directed to only one person at a time.

You may ask only one question to different persons ,or you can ask different questions.

Its your choice.

[Guest]

You just have to ask a question which can't have an answer, like

"Are you going to say no?"

Yes will say yes, No will say no and Truth teller's head will explode. or maybe he will say, I can't answer that.

[Guest]

First Questions: Do you always answer yes?

If the answer is yes, you know this is the Yes Answerer and you move on to another person

If the answer is no, this is either the truth teller or the No Answerer and you stay with the first person

Second Question asked to person listed above: Do you ever answer yes?

If the answer is yes, you know this is the truth teller

If the answer is no, you know this is the No Answerer

Third Questions asked to a new person: Do you always answer no?

If the answer is yes, this person is the Yes Answerer (first questions must have been answered no)

If the answer is no, this person is the other possibility from the second question

If the answer to the first question is yes, you don't need a third question since it just determines a Yes Answerer.

If the answer to the first question is no, you need a third questions since it provides the ability to determine a second person.

Once you have two of the people figured out the third is available.

[wolfgang]

You just have to ask a question which can't have an answer, like

"Are you going to say no?"

Yes will say yes, No will say no and Truth teller's head will explode. or maybe he will say, I can't answer that.

[Guest]

First, ensure that the three people are standing in some order and that the order does not change during your questioning.

Next, you ask the first person what the second person always answers with. Then, ask the second the same question of the third. Finally, ask the third the same question of the first person.

This generates a unique set of answers for each possible order of persons:

T=truth teller, Y=yes man, N=no man

Order - Answers

TYN - YYN

TNY - NNY

YTN - YNN

YNT - YNY

NTY - NYY

NYT - NYN

Based on the order of answers, you now know who's who.

Edited November 18, 2010 by Egghead

[phaze]

Question 1 to man on left is the man you are standing next to a yes man?

Question 2 to man on right is the man you are standing next to a nay sayer?

if you get two yes's you know it is YNT

if you get two nos you know it is NYT

If you got a Yes (Q1) and a No(Q2) ask the middle man

Question 3a Are you a nay sayer?

If yes it is TYN else it is YTN

If you got a No (Q1) and a Yes(Q2) ask the middle man

Question 3a Are you the truth teller?

If yes it is NTY else it is TNY

Is it possible to always ask less than 3 questions? If so how and if not why.

[Guest]

nicely played huevo

[Guest]

Is it possible to always ask less than 3 questions? If so how and if not why.

There are six possible scenarios (TYN, TNY, YTN, YNT, NTY and NYT) and the only responses you can receive are yes or no. Thus, the possible answer sets from asking two questions are YY, NN, YN and NY. Therefore, at least one answer set will define more than one order of people. Unless you have some other input such as hesitation when answering a difficult question or the possibility of no answer at all, then three questions must be asked.

Please note that three questions with a yes or no answer would produce a total of eight (or 2^3) answer sets; whereas the extra input with two questions would produce six (or 3^2) answer sets. You need at least as many answer sets as there are scenarios to determine which scenario results in a particular answer set. I hope I haven't confused anyone and if I happen to be incorrect somewhere, please point it out.

nicely played huevo

If my Spanish is not too rusty, thank you; or, in my best Spanish accent, gracias mi amigo.

Edited November 18, 2010 by Egghead

[Guest]

I asked the first man a set of contradictory questions, i.e.:

Ask "A" is person B the yes man?

Ask "A" is person B the no man?

If his two answers are identical, then that is the person he is. If his two answers are different, you know he is the truth teller, and you know who person B is based on his answers, which also gives you person C by process of elimination.

If his answers are the same, you must then ask a question of one of the other two men that you know to be true or false, depending on who you are looking for.

If you are looking for the yes man, you may go up to person B and ask "Is your shirt red (even though you know his shirt is blue)? " if he answers yes, then he is the "yes" man, if he answers "no" he is the truth teller.

[Guest]

Question 1: Ask a random first guy: Is X true?

where X is any proposition that can elicit a yes or no answer if asked of the truth teller (for instance, X = you are the Yes guy; or X = color of your hair is hot pink or X = your name is Rumpelstiltskin).

Question 2: Again to the first guy: Is X untrue?

Analyze: If answers are: (Yes,Yes), first guy is the Yes guy. If (No,No) first guy is the No guy. If the answers change, first guy is the truth teller. At this point the identity of the first guy is revealed.

Question 3: a) If first guy is the truth teller, ask him if a random second guy is the Yes guy?

Analysis: As he answers truthfully, the identities of the other two guys are revealed. Done!

b)If the first guy is not the truth teller, ask a random second guy: is the first guy the Yes guy?

Analysis: Note that you already know the identity of the first guy. If the answer from the second guy coincides with what you know then the second guy is the truth teller. If it contradicts, the second guy is the opposite of the first guy, i.e., he is the No guy if the first guy = Yes or he is the Yes guy if the first guy = No.

[Guest]

[Guest]

Let T=True man Y=yes man and N=No man

One can pick the three men in 6 possible ways.

N T Y => Ask is 1=1 if he says no you know for sure he is N man and the rest two are T and Y. Ask is 1>1 to any one of the remaining two and if he answers correctly he is T or else he is Y.

N Y T => same as above case

T N Y => As is 1=1 if he says yes then he is either Y or T men, to find out who he is ask him if 1>1 and if he says correctly then he is T or else he is Y.

T Case: If he is T then the remaining are Y and N, ask any one of remaining if 1=1 and if he answers correct he is the Y or else he is N.

Y Case: if he is Y then the remaining are T and N, ask any one of remaining if 1=1 and if he answers correct he is the T or else he is N.

T Y N => same as above case

Y T N => same as above case

Y N T => same as above case

---

Cheers

Edited November 19, 2010 by Srikanth Mujjiga

[Guest]

Simply ask them their names, truth teller will tell his name while the other two would reply only yes or no!

[Guest]

Simply ask them their names, truth teller will tell his name while the other two would reply only yes or no!

You can only do this if truth teller's name is Yes or No (per OP)...then it wouldn't help much.

[wolfgang]

Let T=True man Y=yes man and N=No man

One can pick the three men in 6 possible ways.

N T Y => Ask is 1=1 if he says no you know for sure he is N man and the rest two are T and Y. Ask is 1>1 to any one of the remaining two and if he answers correctly he is T or else he is Y.

N Y T => same as above case

T N Y => As is 1=1 if he says yes then he is either Y or T men, to find out who he is ask him if 1>1 and if he says correctly then he is T or else he is Y.

T Case: If he is T then the remaining are Y and N, ask any one of remaining if 1=1 and if he answers correct he is the Y or else he is N.

Y Case: if he is Y then the remaining are T and N, ask any one of remaining if 1=1 and if he answers correct he is the T or else he is N.

T Y N => same as above case

Y T N => same as above case

Y N T => same as above case

---

Cheers

good!!

[wolfgang]

Simply ask them their names, truth teller will tell his name while the other two would reply only yes or no!

but this question isn`t(yes or no)question..

[Guest]

Here's the question i would ask

i would ask each fellow my name

So now the "YES" fellow would say yes; The "NO" guy would say no, And the honest man would say it......

QUITE EASY HUH!!

LOVE IT!!

[k-man]

Here's the question i would ask

i would ask each fellow my name

So now the "YES" fellow would say yes; The "NO" guy would say no, And the honest man would say it......

QUITE EASY HUH!!

LOVE IT!!

You might as well ask today's date, but the OP clearly states that the questions must be Yes/No questions.

[Guest]

First guy : Are you a YES man.

If he says Yes, then he is a Yes Man.

Go on to guy number Two, and ask him if he is the truth man. If he says Yes, then you found truth man. If he says No, then he is No man.

Now, the other scenerio,

Guy #1 Ask, are you the Yes man. He says No.

So he could either be the truth teller, or the No man.

Guy #2 Are you the truth teller, if he says Yes, he could be the yes man or truth man, depends on who is #3

ask guy #3 are you the Yes man, now if he says Yes, then guy #2 is truth. If he says No, then guy #3 is truth, guy #2 is Yes, guy #1 is No man.

Edited November 25, 2010 by Ionno