You are to meet with two brothers. You know that one of them, named Bob, has a very important package for you. Unfortunately, you never saw Bob or his brother, and don't know who is who.
To make the matter worse, one of the brothers is a pathological liar who never tells the truth, while the other never lies. Not only do you not know which is the liar and which tells the truth, but also, you do not know wether Bob is the liar or not.
Upon meeting the brothers, you can ask one short question of either of the brothers (but not both) to establish with certainty which of the two is Bob. (It is possible to do this with a question of four to five words.)
What question would you ask?
(In reply to
Puzzle Solution by K Sengupta)
After Bob 's identity has been correctly established, he should be asked this question: "If I told you that you are a knight, would you answer "Yes"?"
If Bob is the knight, he he will truthfully say "Yes"
If Bob is the liar, he will be forced to lie about his intent to speak falsely, and will answer "No" which is the truth.
Consequently, the response to the above query will accurately pinpoint Bob's type.
Edited on February 27, 2022, 1:55 am
Puzzle Solution: Identifying Bob's Type
