请教另一题

wretdgdh

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 ?

A. 16%

B. 32%

C. 48%

D. 84%

E. 92%

答案是D 怎么做啊

谢谢

himba

这是方差里面2个典型考法里面的一个，搜索一下，你就会发现很多解释了。