Kenneth Rosen Edition 6th Exercise 1.2 Question 15 (Page No. 23)

Question

Each inhabitant of a remote village always tells the truth or always lies. A villager will give only a “Yes” or a “No” response to a question a tourist asks. Suppose you are a tourist visiting this area and come to a fork in the road. One branch leads to the ruins you want to visit; the other branch leads deep into the jungle. A villager is standing at the fork in the road. What one question can you ask the villager to determine which branch to take?

Answer 1

The answer is apparently: "If I were to ask you whether the right branch leads to the ruins, would you answer yes?"

Explanation:

For the sake of simplicity suppose the left branch leads to the ruins whereas the right one leads you lost deep into the jungle.

Case 1. The villager is a liar: in this case, since he knows the right branch leads to the jungle then he'd say it leads to the ruins, but he won't tell you NOW this, so his answer here is NO.

Case 2. The villager tells the truth: he will answer NO again, 'cause he knows the right branch takes you to the jungle and he will let you k now that.

From the above, it's clear you must choose THE other branch if the answer is NO. 

Comments

Sir, I am not a Gate 2023 aspirant.

---

@pavan singh

This Exercise 1.2 Q 15 question is some game-puzzle type of question, in which our aim should be to “understand the solution once it is provided to us”.

As the best selected answer says “The answer is apparently….”, then we try to understand it.

There is NO problem if you could not come up with the given solution. If you share this question to some mathematician, they would not spend a single second on it & declare it silly children play.

---

@Deepak Poonia ok thanks Sir.....