Peter and paul.

[AxyGaming]

Peter and Paul are brothers. One of them, we don't know which, always lies; the other always tells the truth. I ask one of them: "Is it Paul that lies"?


"Yes" he answers.

Did I speak to Peter or Paul?

[Sora]

SPOILER:

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Oh man, that's a puzzle.
So we have two brothers,
1) Peter
2) Paul

You ask one of them.
Scenario 1: You ask Paul "Is it Paul that lies"?
1.1: Paul would answer no because he always lies
1.2: Paul would answer no because he speaks the truth

Scenario 2: You ask Peter "Is it Paul that lies"?
2.1: Peter would answer yes because he always lies
2.2: Peter would answer no

If Paul is the liar, he would answer: No
If Paul is not the liar, he would still answer: No (truthfully)

If Peter is the liar, he would answer: Yes
If Peter is not the liar, he would answer: No

So from that combination, since one of them always has to lie, and the answer is "Yes", Peter lies and is the one you spoke to?

[Supergirl]

(09-28-2018, 05:23 PM)Sora Wrote: SPOILER:

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Oh man, that's a puzzle.
So we have two brothers,
1) Peter
2) Paul

You ask one of them.
Scenario 1: You ask Paul "Is it Paul that lies"?
1.1: Paul would answer no because he always lies
1.2: Paul would answer no because he speaks the truth

Scenario 2: You ask Peter "Is it Paul that lies"?
2.1: Peter would answer yes because he always lies
2.2: Peter would answer no

If Paul is the liar, he would answer: No
If Paul is not the liar, he would still answer: No (truthfully)

If Peter is the liar, he would answer: Yes
If Peter is not the liar, he would answer: No

So from that combination, since one of them always has to lie, Peter is the liar?

I like your analyse about, but I would shorten it, because of "Is it PAUL that lies?", seem for me he spoke to Peter, because he used "Paul" in his question 

If he would have spoken to Paul he would have used "Is it you that lies?".

Just an other way / sight, but maybe my english is to bad to understand it correct (as I tried to explain) 

But I am happy we came to the same result 



Hopefully we are both not wrong, but maybe we are ... many of such riddles have a "surprise" ?

Edit: just noticed, you cleared who is the liar, but he asked "Did I speak to Peter or Paul?", maybe that is the "surprise" 

[Squirrel]

(09-28-2018, 02:34 PM)AxyGaming Wrote: Peter and Paul are brothers. One of them, we don't know which, always lies; the other always tells the truth. I ask one of them: "Is it Paul that lies"?


"Yes" he answers.

Did I speak to Peter or Paul?

I used to love these logic puzzles!  If there were two statements, you could turn it into two boolean equations, and then just solve the variables.

My mind wants to go through the 4 combinations (2 brothers X 2 types), but alas my brain has grown lazy with age!

C'mon, someone here has to be able to get it.

If it's still unsolved when I get up tonight, I'mma have to try to destroy it. lol

[AxyGaming]

(09-28-2018, 05:23 PM)Sora Wrote: SPOILER:

------------------
Oh man, that's a puzzle.
So we have two brothers,
1) Peter
2) Paul

You ask one of them.
Scenario 1: You ask Paul "Is it Paul that lies"?
1.1: Paul would answer no because he always lies
1.2: Paul would answer no because he speaks the truth

Scenario 2: You ask Peter "Is it Paul that lies"?
2.1: Peter would answer yes because he always lies
2.2: Peter would answer no

If Paul is the liar, he would answer: No
If Paul is not the liar, he would still answer: No (truthfully)

If Peter is the liar, he would answer: Yes
If Peter is not the liar, he would answer: No

So from that combination, since one of them always has to lie, and the answer is "Yes", Peter lies and is the one you spoke to?

Quite right, sora ,Neither of them can say that they are lying. If he were the liar, he'd be telling the truth; and if he were not the liar, he'd be lying - a contradiction. So Paul couldn't answer the question: he can't say that he is the liar, nor can he say that he is not. So it must be Peter who answers, as you say. I went round in circles before I settled this one, but got there in the end.