填空题
设X～N(1，4)，Y～B(3，
【正确答案】
【答案解析】
[解析] P{XY+1＞X+Y}=P{(X-1)(Y-1)＞0}
=P{X＞1，Y＞1}+P{X＜1，Y＜1}
=P{X＞1}P{Y＞1)+P{X＜1}P{Y＜1}
=
(P{X=2}+P{X=3})+
P{X=0}
[解析] P{XY+1＞X+Y}=P{(X-1)(Y-1)＞0}
=P{X＞1，Y＞1}+P{X＜1，Y＜1}
=P{X＞1}P{Y＞1)+P{X＜1}P{Y＜1}
=
(P{X=2}+P{X=3})+
P{X=0}