51. (3) In the family, besides the father and mother, there are two children. Everyone calls each other by their names. It is customary, when addressing one's child or parent, to list all those mentioned from the youngest to the oldest, and in conversations between children or between parents - the opposite. Lёsha said to Svetlana: “We are going to the theater: Nastya, I, and Volodya.” What are the names of the father and mother?
- Answer: Vova and Svetlana. Let's assume the father is Lёsha. Then Vova is younger, which means Lёsha listed from the oldest to the youngest. Therefore, Nastya is older than Lёsha, so Nastya is the mother. But listing from the oldest to the youngest, Lёsha could only be addressing the mother. Contradiction. Therefore, Lёsha is the son, and the father is Vova. Then Lёsha listed from the youngest to the oldest, which means he was addressing the mother. Thus, the mother is Svetlana.

(A. Shapovalov)