设 sim N((M)_(1),({O)_(1)}^2),Ysim N((M)_(2)cdot ({O)_(2)}^2) ,且X与Y相互独立,设 =dfrac (X+Y)(2) ,则Z服从 ()-|||-(A) ((mu )_(1)+(mu )_(2),({sigma )_(1)}^2+({sigma )_(2)}^2) ; (B) ((mu )_(1)+(mu )_(2),dfrac ({{sigma )_(1)}^2+({sigma )_(2)}^2}(2)) ;-|||-(C) (dfrac ({mu )_(1)+(mu )_(2)}(2),dfrac ({{sigma )_(1)}^2+({sigma )_(2)}^2}(2)) ; (D) (dfrac ({mu )_(1)+(mu )_(2)}(2),dfrac ({{sigma )_(1)}^2+({sigma )_(2)}^2}(4)) .

4.设随机变量X与Y相互独立,且-|||-.sim N((M)_(1),({sigma )_(1)}^2) , sim N((M)_(2),({O)_(2)}^

设Xsim N(0,1), Ysim chi^2(n), 且X与Y相互独立, 则Z=(X)/(sqrt(Y/n))simA. 自由度为$n$的卡方分布B. 自由

9 单选设总体 sim N((M)_(1)({O)_(1)}^2) sim N((mu )_(2),({sigma )_(2)}^2), X与Y相互独立,-||

设Xsim N(0,1),Ysim x^2(n)，且X,Y相互独立，则(X)/(sqrt(Y))sqrt(n)simA. F(1,n)B. F(n,1)C. t

设 X sim N(2,1)，Y sim N(-1,1)，且 X 与 Y 相互独立，令 Z = 3X - 2Y - 6，则 Z sim ( )。A. $N(2,

设随机变量 X sim N(2, 4), Y sim N(1, 1), 且 X, Y 相互独立, 则 Z = X - 2Y + 3 sim ( )A. $N(7

设总体X与Y相互独立，sim N(3,({O)_(1)}^2) sim N(-2,({O)_(2)}^2)，从X中抽得简单随机样本：sim N(3,({O)_(

设sim N(1,2)，sim N(1,2)，且X与Y相互独立，则sim N(1,2)________.设，，且X与Y相互独立，则________.

设X~N(1, 2), Y~N(-1, 3)，且X与Y相互独立，则2X-Y~( )A. N(3, 8)B. N(3, 5)C. N(3, 11)D. N(3,2

设X与Y相互独立,且 sim N(0,1) sim (x)^2(5),-|||-则=dfrac (X)(sqrt {Y/4)}