某项竞赛分为初赛、复赛、决赛三个阶段进行,每个阶段选手要回答一个问题.规定正确回答问题者进入下一阶段竞赛,否则即遭淘汰.已知某选手通过初赛、复赛、决赛的概率分别是
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,
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,
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,且各阶段通过与否相互独立.
(Ⅰ)求该选手在复赛阶段被淘汰的概率;
(Ⅱ)设该选手在竞赛中回答问题的个数为ξ,求ξ的数学期望和方差.
考点分析:
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