1. Is it possible to arrange the natural numbers from 1 to 9 (each used once) in the cells of a $3 \times 3$ table so that the sum of the numbers in each row is divisible by 9 and the sum of the numbers in each column is divisible by 9? (20 points)
Solution: Yes, for example like this:

| 1 | 3 | 5 |
| :--- | :--- | :--- |
| 8 | 4 | 6 |
| 9 | 2 | 7 |

Answer: it is possible