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问题 解答题

甲、乙两人进行一场乒乓球比赛，根据以往比赛的胜负情况知道，每一局比赛甲胜的概率0.6，乙胜的概率为0.4，本场比赛采用三局两胜制．

（1）求甲获胜的概率．

（2）设ξ为本场比赛的局数，求ξ的概率分布和数学期望．

答案

（1）甲获胜分为两种情况，即甲以2：0获胜或以2：1获胜，

甲以2：0获胜的概率为P1=0.62=0.36

甲以2：1获胜的概P2=C21×0.6×0.4×0.6=0.288

故甲获胜的概率为P=P=0.36+0.288=0.648

（2）由题意知ξ的取值为2，3．

P（ξ=2）=0.62+0.42=0.36+0.16=0.52

P（ξ=3）=C210.62?0.4+C210.42?0.6=0.288+0.192=0.48

∴ξ的分布为

 ξ 2 3
 P 0.52 0.48
∴E（ξ）=2×0.52+3×0.48=2.48．

单项选择题

物体借助运力在空间上产生的位置移动称为()。

A．装卸

B．搬运

C．运输

D．保管
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阅读理解

Smoking, which may be a pleasure for some people, is a series of discomfort for their fellows. Medical scientists have expressed their concern about effect of smoking on the health not only of those who smoke but also those who do not smoke. In fact, non-smokers who take in the air polluted by tobacco smoke suffer more than the smokers themselves. A great number of students are trying to persuade the university to forbid smoking in classrooms. Believe they are completely right in their aim. However, I think it more important to achieve this by calling on the smokers to use good judgment and to show concern for others. Smoking is not allowed in theaters, cinemas and in other public places. Therefore, smoking must be forbidden in our classroom. Although many people have passed away for having smoked a lot and we call on people to give up smoking, yet many more that are following will turn down what we say every day, above all, the young people smoke a lot more.

小题1: In the writer’s opinion, smoking does good to ________.

A．nobody

B．some people

C．smokers

D．young people小题2: The phrase “pass away” probably means ________.

A．leave one’s home

B．lose one’s life

C．pass by

D．go away小题3:According to the selection, which of the following is true?

A．Smokers suffer from the polluted air more than the non-smokers.

B．Non-smokers suffer from the polluted air more than the smokers.

C．Non-smokers suffer as much from the polluted air as the smokers.

D．Non-smokers don’t suffer so much from the polluted air as the smokers.
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