应睁碧用全概率公式,一年悉庆举内获得概率P1为(1/2)*(1/2)=1/4;两年获得概率差耐P2为2*(1/2)*(1-1/2)*(3/4)+(1-1/2)*(1-1/2)*(2/3)*(2/3)=3/8+1/9=35/72;故总概率为两者相加,即53/72。X 2 3 4 P(X)1/4 1/2 1/4E(X)=3