问题 解答题
中、日两国争夺某项国际博览会的申办权,进入最后一道程序,由国际展览局三名执委投票,决定承办权的最后归属.资料显示,A,B,C三名执委投票意向如下表所示
国别概率执委中  国日  本
A
1
3
2
3
Bxy
C
3
4
1
4
规定每位执委只有一票,且不能弃权,已知中国获得两票的概率为
5
12

(1)求x,y的值;(2)设中国获得的票数为ξ,试写出ξ的概率分布列,并求Eξ.
答案

(1)由题意可得:x+y=1,…①

∵中国获得两票的概率为

5
12

1
3
•x•
1
4
•+
1
3
• (1-x)•
3
4
+
2
3
•x•
3
4
=
5
12
,…②

由①②可得:

x+y=1
1
3
•x•
1
4
+
1
3
•y•
3
4
+
2
3
•x•
3
4
=
5
12

解得x=y=

1
2

(2)由题意可得:ξ可能取的值为:0,1,2,3,

∴P(ξ=0)=

2
3
×
1
2
×
1
4
=
2
24
=
1
12
,P(ξ=1)=
1
3
×
1
2
×
1
4
+
2
3
×
1
2
×
1
4
+
2
3
×
1
2
×
3
4
=
9
24
=
3
8

P(ξ=2)=

1
3
×
1
2
×
1
4
+
1
3
×
1
2
×
3
4
+
2
3
×
1
2
×
3
4
=
10
24
=
5
12
,P(ξ=3)=
1
3
×
1
2
×
3
4
=
3
24
=
1
8

∴ξ的分布列为:

ξ0123
P
2
24
9
24
10
24
3
24
∴ξ的数学期望为:Eξ=0×
2
24
+1×
9
24
+2×
10
24
+3×
3
24
=
19
12

阅读理解

阅读理解

     Andra Rush,a member of the Mohawk Indian tribe (部落) of Ontario,Canada,was raised 30 miles

outside Detroit,not far from her grandparents and their Ontario reservation (印第安人保留地).When

the teenage Rush visited the reservation for the first time,she was struck by the poverty and lack of hope.

"I really wanted to make a difference,"she says.

     She graduated  from  the University of  Michigan in 1982  and took a nursing job . But she was

disappointed with the low pay,and within a year she was pursuing an MBA.That summer,she interned

(作实习生) at an air freight (货运) company,where the speed of package pickups and deliveries drove

profits."I thought I could do that better," Rush says.

     She used her credit cards and borrowed $5,000 from her parents to buy a van and two used pickup

trucks.She accepted every delivery job that came her way,and worked nursing shifts on weekends.

Within six months,Rush had ten employees,and customers like Ford and GM were paying her to fetch

small packages from the airport.Ford was the first to offer her a job trucking parts between its plants and

suppliers.

     Rush_kept_a_single-minded_focus_on_meeting_deadlines-no matter what.In the wake of 9·11,when

increased security stalled (拖延)  traffic for hours on Detroit's  largest  bridge, she hired ships to get  her

trucks across the Detroit River.

     By 2001,many of Rush's 1,000 employees were Native Americans,working alongside people of every

background.But she felt she hadn't done enough.So she joined forces with a Canadian parts maker to

design and fit auto parts.She located the plants near reservations,creating opportunities where they were

needed most.By 2009,her auto parts business was bringing in $370 million.

     Rush is 49 now and still working hard."I love my job,"she says."I like the fact that you can keep

challenging yourself-and then suddenly you lift your head and it's been 25 years."

1.When first visiting the reservation,young Rush felt__________.

A.sorry        

B.pleased

C.nervous  

D.curious

2.After her internship at the air freight company,Rush__________.

A.acquired an MBA

B.started a transport business

C.worked as a full-time nurse

D.became a worker at the airport

3.The underlined part in Paragraph 5 means that__________.

A.Rush was never late for meetings

B.Rush believed in the importance of meetings

C.Rush tried hard to guarantee on-time deliveries

D.Rush would accept every delivery job

4.We learn from the passage that Rush__________.

A.only employs Native Americans in her company

B.is the owner of a famous international auto maker

C.believes she would do better if she had better opportunities

D.tries hard to help Native Americans on reservations

5.The underlined word "they" in Paragraph 6 refers to__________.

A.Native Americans  

B.parts

C.reservations  

D.opportunities

单项选择题 A1型题