(1)3件中恰有1件次品的概率 C(4,1)*C(36,2)/C(40,3)=4*36*35*3/(40*39*38)≈0.2551
(2)3件全是正品的概率 C(36,3)/C(40,3)=36*35*34/(40*39*38)≈0.7227
(3)3件中至少有1件次品的概率 1-C(36,3)/C(40,3)≈0.2773
(4)3件中至少有2件次品的概率 C(4,2)*C(36,1)/C(40,3)+C(4,3)/C(40,3)≈0.0223