甲,乙,丙三位同学独立完成6道数学自测题,他们答题及格的概率依次4/5,3/5.7/10.三人中有且只有俩人及格的概率.
6个回答

(4/5)*(3/5)*(3/10)+(4/5)*(7/10)*(2/5)+(1/5)*(3/5)*(7/10)

=(36+56+21)/250

=113/250

1-(4/5)*(3/5)*(7/10)

=1-84/250

=166/250

=83/125