### Brain Teasers

# Truths and Lies

There are three persons in a room.

One of them always tells the truth, but the others are "alternate liars": they tell the truth then lie, then truth, etc, but you do not know if they will start by telling the truth or a lie...

You can ask three questions that MUST be answered by Yes or No.

Find the truth teller.

One of them always tells the truth, but the others are "alternate liars": they tell the truth then lie, then truth, etc, but you do not know if they will start by telling the truth or a lie...

You can ask three questions that MUST be answered by Yes or No.

Find the truth teller.

### Hint

Ask the questions to one person only.### Answer

Q1. Mr. A, are you a truth teller?- Yes

or

- No.

Q2. Mr. A, are you a truth teller?

- Yes

or

- No.

Q1: Q2:

Yes Yes: A is the truth teller.

Yes No : A is an alternate liar, next answer is a lie.

Q3: Mr. A, is B the truth teller?

- Yes: C is the truth teller.

- No: B is the truth teller.

No Yes: A is an alternate liar, next answer is true.

Q3: Mr. A, is B the truth teller?

- Yes: B is the truth teller.

- No: C is the truth teller.

No No : Impossible.

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## Comments

You didn't say if the three knew each other, and therefore who the liars were.

what?

crazy teaser

crazy teaser

good one well thought out

the obvious answer is to ask them all several obvious yes-no questions!!!!!!!!!!!!

"No Yes: A is an alternate liar, next answer is true. "

If Mr. A answers "No" the first time he is asked if he is a true teller than you do not need to ask it again (since a true teller would never answer no) and you know his next answer will be a lie.

Otherwise a very clever teaser and well written answer.

If Mr. A answers "No" the first time he is asked if he is a true teller than you do not need to ask it again (since a true teller would never answer no) and you know his next answer will be a lie.

Otherwise a very clever teaser and well written answer.

I'm a little confused.

It seems as if you can do it in 2 questions. Ask "A" and "B" the following question:

Did you lie the last time you were asked a question?

A truth teller will say no, and an alternate liar will say yes. It doesn't matter where they are in the cycle. So if you get two yesses, it's C; if you get a no, that's the truth teller. What am I missing here?

Did you lie the last time you were asked a question?

A truth teller will say no, and an alternate liar will say yes. It doesn't matter where they are in the cycle. So if you get two yesses, it's C; if you get a no, that's the truth teller. What am I missing here?

One question (asked twice)!

You simply ask them all any yes/no question. e.g. "Is this a red shirt?" Note their answers, and ask the question again. Two will change their answers; one will keep it the same.

You simply ask them all any yes/no question. e.g. "Is this a red shirt?" Note their answers, and ask the question again. Two will change their answers; one will keep it the same.

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