X( 1？ y)( 1？ z)=0.08xy( 1？ z)=0. 12 1？ ( 1? x)( 1？ y)( 1？ Z) = 0.88 x = 0.4y = 0.6z = 0.5。
So the probability of student Xiao Zhang getting an A is 0.4.
(ii) If the function f(x)=x2+ξx is an even function on r, ξ=0.
When ξ=0, it means that Xiao Zhang has chosen three courses or none.
∴p(a)=p(ξ=0)=xyz+( 1-x)( 1-y)( 1-z)=0.4×0.5×0.6+( 1-0.4)( 1-0.5)( 1-0.6)=0.24
The probability of event A is 0.24.
(iii) according to the meaning of the question, ξ = 0,2.
Then the distribution list of ξ is
ξ 0 2p0.24 0.76 ∴ξis's mathematical expectation Eξ=0×0.24+2×0.76= 1.52.