数学奇差的我想请教一道OG题

lanxigmat

刚刚开始做数学，绿皮数学的第70题:

If a certain sample of data has a mean of 20.0 and a standard deviation of 3.0,which of the following values is more than 2.5 standard deviation from the mean?

题目都读不懂。。。。

joe_gross

统计学过吗

lanxigmat

没。。。。

kevin070707

If a certain sample of data has a mean of 20.0 and a standard deviation of 3.0,which of the following values is more than 2.5 standard deviation from the mean?

mean=20, one SD=3, then ask what is value more than 2.5SD?

20+2.5*3=27.5

scutpigus

一个标准偏差是3.0, 求选项中哪个是超过2.5个标准公差的.

先求不超过2.5个标准公差的范围,设为x:

一个标准公差为3, 那么2.5个标准公差值就为2.5*3=7.5

20-7.5<x<20+7.5

得出:12.5<x<27.5

所以选项A,12为答案