题目

Dangerous Sports Around the world more and more people are taking part in danger ous sports and activities．Of course, there have always been people who have looked for adventure—those who have climbed unknown parts of the world or sailed in small boats across the greatest oceans．Now, however, there are people who seek an immediate thrill, a risky activity, which may only last a few minutes or even seconds． I would consider bungee jumping to be a good example of such an activity．You jump from a high place（perhaps a bridge or a hot-air balloon） 200 meters above the ground with an e（本小题共13分） 某校从高一年级学生中随机抽取60名学生，将其期中考试的数学成绩（均为整数）分成六段：，，…，后得到如下频率分布直方图． （Ⅰ）求分数在内的频率； （Ⅱ）根据频率分布直方图，估计该校高一年级学生期中 考试数学成绩的平均分； （Ⅲ）用分层抽样的方法在80分以上（含80分）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，从中任意选取2人，求其中恰有1人的分数不低于90分的概率．