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从8名女生,4名男生中选出3名学生组成课外小组,如果按性别比例分层抽样,则不同的...
从8名女生,4名男生中选出3名学生组成课外小组,如果按性别比例分层抽样,则不同的抽取方法种数为 . (用数字作答)
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④已知随机变量P~N(2,σ
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