题干

网上购物逐步走进大学生活,某大学学生宿舍4人积极参加网购,大家约定:每个人通过掷一枚质地均匀的骰子决定自己去哪家购物,掷出点数为5或6的人去淘宝网购物,掷出点数小于5的人去京东商场购物,且参加者必须从淘宝和京东商城选择一家购物.


(Ⅰ)求这4人中恰有1人去淘宝网购物的概率;

(Ⅱ)用ξ、η分别表示这4人中去淘宝网和京东商城购物的人数,记X=ξη,求随机变量X的分布列与数学期望EX.

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答案(点此获取答案解析)

解:(Ⅰ)依题意,这4个人中,每个人去淘宝网购物的概率为
1
3
,去京东网购物的概率为
2
3

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    I want to admit I'm a bit of a cryer. However, having never really experienced deaths in my life, a few weeks ago I experienced what it means to really, truly, pour my heart out in tears.

    See, my dog was killed by a car right outside my house. Being a witness to this painful event left me in shock for a good hour, but then the floodgates opened. Over the next 48 hours, I might have cried 20 times. Once or twice I crouched(蹲)on the floor with my head in my hands and tears were the only outlet.

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