Q2: A certain characteristic in a large population has a distribution that is symmetric about the mean m. If 68 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m + d ?
If 68 percent of the distribution lies within one standard deviation d of the mean 这句话的意思是 m-d到m+d这个范围里的数据占所有范围的比例是68% m是中线，所有小于m的自然占50% m+d就= 小于m的比例+ m到m+d这个部分所占的比例 即50%+68%/2=84% 画个标准分布的图就明白了
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发表于 2010-10-12 11:32:50
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