P{X=1}=P{恰有一个继电器接通} =P(A1A2)∪(A1A2))=P(A1A2)+P(A1A2) P(AP(A,)+P(AP(A 0.8×0.2+0.2×0.8=0.32 P{X=2}=P{两个继电器都接通} =P(A42)=P(A1)P(A2)=0.8×0.8=0.64转下页 0.8 0.2 0.2 0.8 0.32 ( ) ( ) ( ) ( ) (( ) ( )) ( ) ( ) 1 2 1 2 1 2 1 2 1 2 1 2 =  +  = = + =  = + P A P A P A P A P A A A A P A A P A A P{X=1}=P{恰有一个继电器接通} = P(A1 A2 ) = P(A1 )P(A2 ) = 0.80.8 = 0.64 P{X=2}=P{两个继电器都接通}