Question 17275 – NTA UGC NET JUNE 2023 Paper-1
May 7, 2024Question 13923 – Data-Structures
May 7, 2024Question 12149 – Problem-Solving
In the land of Twitter, there are two kinds of people: knights (also called outragers), who always tell the truth, and knaves (also called trolls), who always lie. It so happened that a person with handle @anand tweeted something offensive. It was not known whether @anand was a knight or a knave. A crack team, headed by Inspector Chitra, rounded up three suspects and interrogated them.
The first interrogation went as follows.
Chitra : What do you know about @anand?
Suspect 1 : @anand once claimed that I was a knave.
Chitra : Are you by any chance @anand?
Suspect 1 : Yes.
The second interrogation:
Chitra : Have you ever claimed you were @anand?
Suspect 2 : No.
Chitra : Did you ever claim you are not @anand?
Suspect 2 : Yes.
The third suspect arrived with a defense lawyer (also on Twitter):
Lawyer : My client is indeed a knave, but he is not @anand.
Suspect 3 : My lawyer always tells the truth.
Which of the above suspects are innocent, and which are guilty?
Explain your reasoning.
Correct Answer: A
knights will not do. Hence Suspect 1 is not Anand.
If Suspect 2 were Anand, then he is either a knight or a knave. If he were a knight, then the answer to question 2 means he claimed he was not Anand, which is a lie.
Hence he is a knave. But then the answer to question 1 is a lie, which means he has once claimed he is Anand, which a liar will not do. This contradiction means that he
is not Anand.
Now Suspect 3 cannot be a knight, since he says his lawyer is truthful, and the lawyer says that he is a knave. So Suspect 3 is a knave. And so what he said is false, and his
lawyer is a knave. But then the lawyer has uttered a falsehood. Of the conjuction he uttered, at least one conjunct is false. But the first conjunct is true, so the second is
false. And Suspect 3 is indeed Anand!