AB分在三人组有C(7,1)*C(6,2)*C(4,2)*C(2,2)/A(3,3)=105
AB分在两人组有C(7,3)C(4,2)C(2,2)/A(2,2)=105
概率为(105+105)/[C(9,3)*C(6,2)*C(4,2)*C(2,2)/A(3,3)]=1/6
AB分在三人组有C(7,1)*C(6,2)*C(4,2)*C(2,2)/A(3,3)=105
AB分在两人组有C(7,3)C(4,2)C(2,2)/A(2,2)=105
概率为(105+105)/[C(9,3)*C(6,2)*C(4,2)*C(2,2)/A(3,3)]=1/6