It is known that there are three weak teams among the eight teams. Now divide these eight teams into two groups, A and B, with four teams in each group, and find the probability that there are exactly two teams in Group A..
The weak team has two C (3,2) combinations, and the strong team has two C (5,2) combinations to form Group A, where C (3,2) C (5,2) = 3x10 = 30, and the total number of possible combinations C (8,4) = 70;
The probability that there are just two weak teams in Group A =30/70=3/7.