If two strong teams are in the same group, two of the six ordinary teams need to be selected from that group.

The number of grouping methods is c (2,6) =15 (species)

The total number of groups is

C (4,8) * C (4,4)/2 = 35 (species) (divided by 2 because A 1-A8 can be divided into (A 1, a2, a3, a4) and (a5, A6, a7, A8) in the process of grouping, too. )

So the possibility is

P= 15/35=3/7