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问题 解答题

某厂工人在2008年里有1个季度完成生产任务，则得奖金300元；如果有2个季度完成生产任务，则可得奖金750元；如果有3个季度完成生产任务，则可得奖金1260元；如果有4个季度完成生产任务，可得奖金1800元；如果工人四个季度都未完成任务，则没有奖金，假设某工人每季度完成任务与否是等可能的，求他在2008年一年里所得奖金的分布列．

答案

设该工人在2008年一年里所得奖金为X，则X是一个离散型随机变量，并且X可能取的值为0，300，750，1260，1800．

由于该工人每季度完成任务与否是等可能的，所以他每季度完成任务的概率等于

1
2
，

所以P(X=0)=

C04
(
1
2
)0(
1
2
)4 =
1
16
，P(X=300)=
C14
(
1
2
)1(
1
2
)3 =
1
4
，P(X=750)=
C24
(
1
2
)2(
1
2
)2 =
3
8
，P(X=1260)=
C34
(
1
2
)3(
1
2
)1 =
1
4
，P(X=1800)=
C44
(
1
2
)4(
1
2
)0 =
1
16

所以X的分布列为

X030075012601800
P
1
16
1
4
3
8
1
4
1
16

阅读理解

阅读理解

       Will it matter if you don't take your breakfast? A short time ago, a test was given in the United States. People of different ages, from 12 to 83, were asked to have a test. During the test, these people were given all kinds of breakfasts, and sometimes they got no breakfast at all. Scientists wanted to see how well

their bodies worked when they had eaten different kinds of breakfasts.

      The results show that if a person eats a right breakfast, he or she will work better than if he or she has no breakfast. If a student has fruit, eggs, bread and milk before going to school, he will learn more quickly and listen more carefully in class.

      The result is opposite to what some people think. Having no breakfast will not help you lose weight.

This is because they are so hungry at noon they eat too much for lunch. They will gain weight instead of

losing it. You will lose more weight if you reduce your other meals.

1. During the test, the people were given_____________.

A. no breakfast at all      

B. different foods or sometimes none

C. very rich breakfasts    

D. little food for breakfast

2. The results show that __________________

A. breakfast has great effect on work and studies.

B. breakfast has little to do with a person's work.

C. a person will work better if he only has fruit and milk.

D. Girl students should have little for breakfast

3. According to the passage, some people think that if you don't have breakfast, you will___________.

A. be healthier    

B. work better    

C. lose weight  

D. lose your way

4. The word "reduce" in the last sentence means__________.

A. 增加    

B. 减少    

C. 放弃    

D. 享用

5. Which of the following is NOT right?

A. It is bad for your health to have no breakfast

B. Too little for breakfast and too much for lunch may make you fatter.

C. If you don't eat much for lunch and supper, you may lose weight.

D. The more breakfast you have, the more quickly you'll learn in class.
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填空题

群落的水平结构是指群落在水平方向的（）。
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