急问一道prep数学，不明白啊

vivianxiaopi

 

33. 9.4, 9.9, 9.9, 9.9, 10.0, 10.2, 10.2, 10.5

the mean and the standard deviation of the 8 numbers shown are 10 and 0.3, respectively. what persentage of the 8 number's are within 1 standard deviation?

A) 90% B) 85% C) 80% D) 75% E) 70%

答案是D thanks a lot~~~

thanks a lot~~~

thanks a lot~~~

gelan1234

我也完全不明白，顶一下，请大牛牛出来回答一下！

我的理解是        (X^2-10^2)/2开根号<0.3 但是算不出来70％！

anistonlucky

9.7<x<10.3

6/8=75%