[数学] 哪位朋友能帮忙解题呵，谢谢啦。

Five classes A, B, C, D and E took part in an international chess competition.
Each class sent in 2 participants.
The rules of the competition were :
(a) Participants do not compete with each other for more than 1 game,
(b) Participants from the same class cannot compete with each other.
After a few rounds of competitions, it turned out that all had completed different number of games, except for a participant from class A.
How many games had the 2 participants from class A completed?.

8, each participtes 4.

clues:
a. all possible different numbers: 0,1,2,3,4,5,6,7,8.
b. each class participates 8 games..

THANK YOU VERY MUCH..