There are 25 teams in the tennis competition, and the top 8 players are decided by group round robin and knockout. How to arrange them? Use two balls in each game. * * * How many balls do you need?

Three teams in each group, four teams in each group, and then draw lots to eliminate them. Counting balls is so simple that any junior high school student can work it out. . . Three teams in each group play three games of 3 * 2, seven teams of 7*3*2 and four teams of 6*2. 4+2+ 1 match of 8 teams in the knockout stage (excluding ranking 5-8 and ranking 3 and 4), total; 7*3*2+6*2+(4+2+ 1)*2