4. In the record of three two-digit numbers, there are no zeros, and in each of them, both digits are different. Their sum is 40. What could be their sum if the digits in them are swapped?
Answer: 103.

Solution. In all numbers, the tens digit is 1. Otherwise, the larger number is at least 21, and the other two are at least 12. Their sum is no less than $12+12+21=44$, which is not equal to 40. The sum of the units digits is 10 (zeros are not allowed). Therefore, the sum of the numbers with swapped digits is 103.

There are only three possible sets of numbers: $12,12,16$ or $12,13,15$, and 13, 13, 14. (This can justify the answer)

Criteria. Answer with one or two examples: 1 point.

Answer with three examples, but without proof that there are no others: 2 points.

Complete solution: 7 points.