4. Sasha went to visit his grandmother. On Saturday, he got on the train, and after 50 hours on Monday, he arrived at his grandmother's city. Sasha noticed that on this Monday, the date matched the number of the carriage he was in, that the number of his seat in the carriage was less than the number of the carriage, and that on the Saturday when he got on the train, the date was greater than the number of the carriage. What were the numbers of the carriage and the seat? Be sure to explain your answer.
Answer. Carriage No. 2, seat No. 1.

Solution. Since the carriage number on Saturday was less than the date, and on Monday it was equal to the date, it is clear that Saturday and Monday belong to different months. Since Sasha traveled for a little more than two days, Monday is the first or second day of the month. Therefore, the carriage number is 1 or 2. However, the carriage number cannot be 1, as the seat number is less than the carriage number. Therefore, Sasha traveled in carriage No. 2, seat No. 1.

## Grading Criteria.

- Correct answer and complete explanation - 7 points.
- Correct answer, but partial explanation - 5-6 points.
- Correct answer, and it is shown how this could happen (dates and change of month), but it is not shown that the answer is unique - 3 points.
- Correct answer, but no explanation - 1 point.