数学题 急啊

xlyun

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%

the answer is D

这道题什么意思啊?看不懂,请NN给指点一下.

企企

应该是1-(1-68%)/2=84%

因为,68%的数都在m-d到m+d之间,又是对称分布的,那么大于m+d的就是32%/2=16%

那么小于m+d的就是1-16%=84%