题干

团购已成为时下商家和顾客均非常青睐的一种省钱、高效的消费方式,不少商家同时加入多家团购网,现恰有三个团购网站在A市开展了团购业务,A市某调查公司为调查这三家团购网站在本市的开展情况,从本市已加入了团购网站的商家中随机地抽取了50家进行调查,他们加入这三家团购网站的情况如下图所示.

(Ⅰ)从所调查的50家商家中任选两家,求他们加入团购网站的数量不相等的概率;

(Ⅱ)从所调查的50家商家中任选两家,用ξ表示这两家商家参加的团购网站数量之差的绝对值,求随机变量ξ的分布列和数学期望;

(Ⅲ)将频率视为概率,现从A市随机抽取3家已加入团购网站的商家,记其中恰好加入了两个团购网站的商家数为η,试求事件“η≥2”的概率.

上一题 下一题 0.0难度 选择题 更新时间:2020-01-13 12:34:15

答案(点此获取答案解析)

解:(Ⅰ)设“从所调查的50家商家中任选两家,他们加入团购网站的数量不相等”为事件A,则 A¯ 表示事件“从所调查的50家商家中任选两家,他们加入团购网站的数量相等”,则P(A)=1﹣P

同类题1

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,选项中有两项为多余选项。

        If you find that your teacher is unfair to you, think about what is happening. Try to find out whether your teacher really dislikes you, or whether something else is going on. Here are some questions to ask yourself:

        ____Ask your classmates if they are having trouble with the teacher, too. If they say yes, perhaps your teacher is to blame.

        Are you working up to your ability? Maybe you got a C in your last test, and your teacher told you that you could do better. And the kid sitting beside you got a C, too.____Isn't this unfair? Well, it could be that your teacher knows that you could do better if you put more effort into it.____

        ____There's nothing wrong with being sensitive(敏感的),but if you react to criticism quite differently from others, this could be a reason why you think your teacher doesn't like you.

        Does your teacher seem to act unfairly all the time, or just once in a while? Think about the harsh(苛刻的) things your teacher has done to you. Are these things happening every day, or just once or twice a month? If your teacher really hates you, you would probably be picked on all the time.____

A  Are you the only person being treated badly, or is your teacher rough on the whole class?

B  Are you getting along well with your classmates? 

C  Are you more sensitive than other students?

D  Are you interested in your lessons?

E  If your teacher has acted unfairly only a few times, then there's probably something else going on.

F  Teachers often grade students by different standards.

G  But the teacher didn't say anything to him!