袋中装有标号分别为1、2、3、4、5、6的卡片各1张，从中任取两张_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题解答题

袋中装有标号分别为1、2、3、4、5、6的卡片各1张，从中任取两张卡片，其标号分别记为x、y（其中x＞y）．

（1）求这两张卡片的标号之和为偶数的概率；

（2）设ξ=x-y，求随机变量ξ的概率分布列与数学期望．

答案

（I）由题意知本题是一个等可能事件的概率，

试验发生包含的事件是从6张卡片中取2张，共有C₆²种结果，

满足条件的事件x、y同奇的取法有C₃²种，同偶的取法有C₃²

∴P=

2

C

23

C

26

=

2

5

（Ⅱ）由题意知变量ξ的可能取值是1，2，3，4，5，

P(ξ=1)=

5

C

26

=

1

3

，P(ξ=2)=

4

C

26

=

4

15

，P(ξ=3)=

3

C

26

=

1

5

，P(ξ=4)=

2

C

26

=

2

15

，P(ξ=5)=

1

C

26

=

1

15

其分布列为

ξ

1

2

3

4

5

P

1

3

4

15

1

5

2

15

1

15

∴Eξ=

5

15

×1+

4

15

×2+

3

15

×3+

2

15

×4+

1

15

×5=

7

3

完形填空

My neighbor’s children love playing hide-and-seek (捉迷藏) as all children do, but no one 36 that a game they played last week would be reported in the local newspaper.
One afternoon, they were playing in the vacant lot (空地)down by the corner. Young Paul, who is only five years old, found the perfect place to 37 . His sister, Natalie, had 38 her eyes and was counting to ten when Paul noticed the mail box at the corner and that the metal door was standing open. The mailman had just 39 several bags of mail and had carried them to his truck which was standing a few feet away. Paul climbed 40 the mail box and pulled the door closed so hard that it 41 . Soon realizing what he had done, he became 42 and started crying. At that time, Natalie was looking for him everywhere but could not find him. It was 43 that she happened to stand at the corner for a minute and heard her brother’s cries. She 44 ran to tell the mailman who hurried back from his 45 to unlock the metal door. Paul was now 46 , but he had such a bad fright that he could not stop crying. The mailman, however, soon found a way of making him 47 again. He told him that the next time he wanted to hide in a mail box, he should remember to put a stamp on himself!

C．immediately

D．post office

多项选择题

以下哪些选项属于会计职业道德修养的境界（）

A.雇佣型境界

B.尽职型境界

C.献身型境界

D.服务型境界