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【简答题】
某校从参加高一年级期中考试的学生中随机抽取60名学生，将其数学成绩（均为整数）分成六段[40，50），[50，60），…，[90，100]后得到如下部分频率分布直方图，观察图形的信息，回答下列问题： （Ⅰ）求分数在[70，80）内的频率，并补全这个频率分布直方图； （Ⅱ）统计方法中，同一组数据该组区间的中点值作为代表，据此估计本次考试的平均分； （Ⅲ）用分层抽样的方法在分数段为[60，80）的学生中抽取一个容量为6的样本，将该样本看成一个总体，从中任取2人，求至多有1人在分数段[70，80）的概率。
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