VTMO 2026 - Grade 3 - Semifinal - SET 2 - Self-study Question 9

Anh writes 1, 2, 3, …, 10 on the board. Bình chooses any seven of these numbers and adds them. Châu independently chooses any seven and adds them. Duy adds Bình’s and Châu’s results. Which cannot be Duy’s result?