1:2都是正品,P=(8/10)*(7/9)=28/45
2:2都是次品,P=(2/10)*(1/9)=1/45
3:一正一次,P=1-28/45-1/45=16/45
4:第2次取出的是次品:P=(8/10)*(2/9)+(2/10)*(1/9)=8/45+1/45=1/5
1:2都是正品,P=(8/10)*(7/9)=28/45
2:2都是次品,P=(2/10)*(1/9)=1/45
3:一正一次,P=1-28/45-1/45=16/45
4:第2次取出的是次品:P=(8/10)*(2/9)+(2/10)*(1/9)=8/45+1/45=1/5