There are three persons in a room. One of them always tells the truth, 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.

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 Today's brain teaser courtesy of Braingle.com.