GATE Civil 2023 Set 1 | GA Question: 4

Question

A duck named Donald Duck says "All ducks always lie."

Based only on the information above, which one of the following statements can be logically inferred with certainty? 

• A. Donald Duck always lies. 
• B. Donald Duck always tells the truth. 
• C. Donald Duck's statement is true.
• D. Donald Duck's statement is false. 

Answer 1

If Donald Duck says, "All ducks always lie," and his statement is true, then it means that ducks, including himself, always lie. However, if all ducks always lie, then his statement must also be a lie. This creates a paradox, as his statement cannot be both true and false simultaneously. Therefore, we can conclude that his statement is false.

So, the correct statement is: "Donald Duck's statement is false."

Correct Answer: C