题干

某学校为了制定治理学校门口上学、方向期间家长接送孩子乱停车现象的措施,对全校学生家长进行了问卷调查.根据从其中随机抽取的50份调查问卷,得到了如下的列联表.

同意限定区域停车

不同意限定区域停车

合计

男

18

7

25

女

12

13

25

合计

30

20

50

(Ⅰ)学校计划在同意限定区域停车的家长中,按照分层抽样的方法,随机抽取5人在上学、放学期间在学校门口参与维持秩序.在随机抽取的5人中,选出2人担任召集人,求至少有一名女性的概率?

(Ⅱ)已知在同意限定区域停车的12位女性家长中,有3位日常开车接送孩子.现从这12位女性家长中随机抽取3人参与维持秩序,记参与维持秩序的女性家长中,日常开车接送孩子的女性家长人数为ξ,求ξ的分布列和数学期望.

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答案(点此获取答案解析)

解:(Ⅰ)由题意知,男性选出 30
5
×18=3
人,

同类题4

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    I am a strong believer that if a child is raised with approval, he will learn to love himself and will be successful in his own way.

    Several weeks ago, I was doing homework with my son in the third grade and he kept standing up from his chair to go over the math lines. I kept asking him to sit down, telling him that he should concentrate better. He sat but seconds later, as if he didn't even notice he was doing it, he got up again. I was getting frustrated, but then it hit me. I started noticing his answers were much quicker and accurate when he stood up. Could he be more intent while standing up?

    This made me start questioning myself and what I had been raised to believe. I was raised to believe that a quiet, calm child was a sure way to success. This child would have the discipline to study hard, get good grades and become someone important in life.

    Now those same people perhaps come to realize that their kids are born with their own sets of DNA and personality traits, and all you can do is loving and accepting them. As parents, throughout their growing years and beyond that, we need to be our kids' best cheerleaders, guiding them and helping them find their way.

    I have stopped asking my son to sit down and concentrate. Obviously, he is concentrating just in his own way and not mine. We need to learn to accept our kids' ways of doing things. Some way may have worked for me but doesn't mean we need to carry it through generations. There is nothing sweeter than being individual and unique. It makes us free and happy and that's just the way I want my kids to live their own life.