随意抛掷一枚均匀的骰子两次，则这两次出现的点数之和为9的概率为（）

A 13．4 B 13．3 C 13．2 D 8．4

A 3 B 6 C 10 D 12

A 2 B 3 C 1 D 4

A 0．4 B 0．6 C 0．3 D 0．5

A E(X)=0．25，D(X)=0．25 B E(X)=0．25，D(X)=4 C E(X)=4，D(X)=4 D E(X)=4，D(X)=0．25

A P(<img src="https://www.beizhujiaoyu.com/uploads/202208/161224065614401.png" width="20" height="35" />∩<img src="https://www.beizhujiaoyu.com/uploads/202208/16122406642811.png" width="20" height="35" />)=1 B P(AB)=P(A)P(B) C P(A)=1-P(B) D P(<img src="https://www.beizhujiaoyu.com/uploads/202208/16122406693211.png" width="20" height="35" />∪<img src="https://www.beizhujiaoyu.com/uploads/202208/16122406642811.png" width="20" height="35" />)=1

A P(<img src="https://www.beizhujiaoyu.com/uploads/202208/161223608767161.png" width="34" height="35" />)=1 B P(AB)=P(A)P(<img src="https://www.beizhujiaoyu.com/uploads/202208/161223609220321.png" width="20" height="35" />) C P(A∪B)=1 D P(A)=1-P(B)

A 都增大 B 都减小 C 都不变 D 一个增大，一个减小

A 0 B <img src="https://www.beizhujiaoyu.com/uploads/202208/161223616828411.png" width="19" height="52" /> C <img src="https://www.beizhujiaoyu.com/uploads/202208/161223617217061.png" width="29" height="52" /> D 3