VTMO 2026 - Grade 4 - Semifinal - SET 4 - Self-study Question 20

Châu has 40 cards numbered from 1 to 40, one of each number. She draws 2 cards. In how many different ways can she draw them so that their sum is divisible by 3? Drawing cards 10 and 2 is the same as drawing 2 and 10.