总分组法=C(9,3)C(6,3)C(3,3)=9!/(3!)^3=8*7*6*5
甲乙在一组的分法=C(7,1)C(6,3)C(3,3)+C(7,3)C(4,1)C(3,3)+C(7,3)C(4,3)C(1,1)
=3*7!/(3!)^2=7*6*5*2
总分组法=C(9,3)C(6,3)C(3,3)=9!/(3!)^3=8*7*6*5
甲乙在一组的分法=C(7,1)C(6,3)C(3,3)+C(7,3)C(4,1)C(3,3)+C(7,3)C(4,3)C(1,1)
=3*7!/(3!)^2=7*6*5*2