自“钓鱼岛事件”，中日关系日趋紧张，不断升级．为了积极响“保_爱下问搜题

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问题解答题

自“钓鱼岛事件”，中日关系日趋紧张，不断升级．为了积极响“保钓行动”，学校举办了一场保钓知识大赛，共分两组．其中甲组满分的有1个女生和3个男生，乙组得满分的有2个女生和4个男生．现从得满分的同学中，每组各任选2个同学，作为保钓行动代言人．

（1）求选出的4个同学中恰有1个女生的概率；

（2）设X为选出的4个同学中女生的个数，求X的分布列和数学期望．

答案

（1）设“从甲组内选出的2个同学均为男同学；从乙组内选出的2个同学中，1个是男同学，1为女同学”为事件A，

“从乙组内选出的2个同学均为男同学；甲组内选出的2个同学中1个是男同学，1个为女同学”为事件B，

由于事件A､B互斥，且P（A）=

C

23

C

12

C

14

C

24

C

26

=

4

15

，P（B）=

C

13

C

24

C

24

C

26

=

1

5

，

∴选出的4个同学中恰有1个女生的概率为P（A+B）=P（A）+P（B）=

4

15

+

1

5

=

7

15

…（5分）

（2）由题意可知：X可能的取值为0，1，2，3，

由（1）可得：P（X=0）=

1

5

，P（X=1）=

7

15

，P（X=2）=

3

10

，P（X=3）=

1

30

∴X的分布列为

X

0

1

2

3

P

1

5

7

15

3

10

1

30

…（10分）

∴X的数学期望：EX=

7

15

+2×

3

10

+3×

1

30

=

7

6

…（12分）

完形填空

阅读下面短文，掌握其大意，然后从36—55各题所给的四个选项(A、B、C和D)中，选出最佳选项，并在答题卡上将该项涂黑。

Last night, when I was driving back home, I noticed a hitchhiker(搭便车的人) who was having no luck getting a ride. I rolled down my 36 and signed to the man to my car. I asked him where he was 37 and he told me he needed a 38 to his doctor’s office which would close in 15 minutes. I told him to 39 and he gratefully did so.
40 he got in he told me that he was a 41 and went out to sea for weeks at a time. He took medicine for his nerves and 42 to get another prescription(处方) before he left on the boat. He said that he had prayed (祈祷) 43 would stop for him so he could be there before the 44 office closed. With some 45 driving we managed to make it there in about 10 46. I then asked him how he 47 on getting back home and he said he could walk. “I’ll patiently 48 for you and bring you back,” I told him. He 49 me and said he should only be about 15 minutes.
Afterwards he got back in my 50 and tried his hardest to pay me back: offering me dinner, gas money, even offering to ship me 40 lbs of scallops (海扇贝)! I 51 refused, gave him a smile card and asked him to help someone else the next time he had a 52. I drove him back to where I had picked him up and 53 one more “thank you” he was on his way.
I feel that the universe 54 provides us with what we need. In the man’s 55 it was a ride, in mine the opportunity to help someone else.

D．Just before

A．teacher’s

C．manager’s

D．captain’s

C．immediately

D．surprisingly

单项选择题

肋

A．由肋骨和肋软骨组成
B．分为真肋和浮肋
C．第8～12对肋形成肋弓
D．第2对肋骨与胸骨角侧面的肋切迹形成关节
E．无上述情况