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%
還是懷疑答案錯,這不是很明顯的答案A嘛?
可是答案是D
不知是否我誤解了,請多多指教,謝謝