VTMO 2026 - Grade 2 - Semifinal - SET 5 - Self-study Question 22

An, Bình, Châu and Dũng have 90 marbles altogether. An and Bình together have three times as many marbles as Châu. An, Bình and Châu together have twice as many as Dũng. How many marbles does Châu have?