问题 解答题
已知某批零件共160个,按型号分类如下表:
型号ABCD
个数2487256
用分层抽样的方法在该批零件中抽取一个容量为20的样本.
(1)应在A型零件中抽取多少个?并求每个A型零件被抽取的概率
(2)现已抽取一个容量为20的样本,从该样本的A型和B型的零件中随机抽取2个,求恰好只抽取到一个B型零件的概率.
答案

(1)每个个体被抽到的概率为

20
160
=
1
8
,24×
1
8
=3,

故应在A型零件中抽取3个,每个A型零件被抽取的概率等于

1
8

(2)按照分层抽样,应从B型的零件中随机抽取1个,

从该样本的A型和B型的零件中随机抽取2个,所有的抽法有C42=6种,

恰好只抽取到一个B型零件的抽法有C31•C11=3种,

故恰好只抽取到一个B型零件的概率等于

3
6
=
1
2

单项选择题 A1型题
阅读理解

阅读表达。

阅读短文,并按照题目要求用英语回答问题。

     In order to be a success in the American business world, you must get along with people. You must

learn to behave yourself in such a way that you earn the affection and respect of others. As we have

already pointed out, Americans mix business and pleasure. Therefore, learning how to chat informally

(非正式地)can be a help with your American business contracts. Americans like to talk about a number

of different topics-sports, politics, cars, popular movies, television shows and personal interests.

     Many large American cities have sports teams. If you are working with Americans in the United

States, it would be a good idea to find out about the local sports teams so that you can join in the almost

inevitable discussions about "What our team will do this year." Politics can be a sensitive topic unless

everyone is of the same mind politically. Limit your discussions to asking questions of your friends. Most

Americans are car owners and some are even obsessive(着迷的)about the subject. You can contribute

to the discussion by talking about cars you have owned or by sharing information you have had in

automotive magazines. Americans watch television almost every night and attend movies regularly, so

naturally TV programs and the latest movies become topics for discussions.

     If you are unable to watch American television or attend American movies, reading the entertainment

section of such magazines as Time and Newsweek will keep you up to date on what is popular in

America.

1. What's the best title of the passage? (No more than 10 words)

   ________________________________________________________________________

2. Why should people be careful with the topic-politics? (No more than 8 words)

   ________________________________________________________________________

3. If you want to keep you up to date on what is popular in America, what should you do?  (No more

    than 10 words)

   ________________________________________________________________________

4. The underlined word "affection" in Paragraph 1 refers to ________.(No more than 4 words)

5. Suppose you are doing business in America, what would you do to be a success in business world?

    (No more than 20 words)

   ________________________________________________________________________

   ________________________________________________________________________