(2*0.9+3*0.8)/(2+3)=84%
(2*90%+3*80%)/(2+3)=82%
(2*90%+3*80%)/(2+3)=84%
设A种有2X个,B种有3X个,合格率等于(2X乘0.9+3X乘0.8)/5X=84%
0.4x0.9+0.6x0.8=0.84
(2*90%+3*80)除以(2+3)=84%