4.P(X>=1)=1-P(X=0)=1-C(2,0)p^0*(1-p)^2=1-(1-p)^2=5/9
p=1/3,p=5/3(舍去)
P(Y>=1)=1-P(Y=0)=1-C(3,0)*(1/3)^0*(2/3)^3=1-8/27=19/27
6.D(Y)=D(X1-2X2+3X3)=D(X1)+4D(X2)+9D(X3)
=6^2/12+4*4+9*3=46
4.P(X>=1)=1-P(X=0)=1-C(2,0)p^0*(1-p)^2=1-(1-p)^2=5/9
p=1/3,p=5/3(舍去)
P(Y>=1)=1-P(Y=0)=1-C(3,0)*(1/3)^0*(2/3)^3=1-8/27=19/27
6.D(Y)=D(X1-2X2+3X3)=D(X1)+4D(X2)+9D(X3)
=6^2/12+4*4+9*3=46