求助数学一题？

叮叮当当

I don't know how to answer this question.

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

a. 12.0

b. 13.5

c. 17.0

d. 23.5

e. 26.5

Thanks a lot , please answer this question as detailed as possible.

himba

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

题意：某个数据样本平均数为20，标准差是3.0，下面哪个值大于平均数+2.5标准差？

因此此数大于20+2.5*3＝27.5？数字选项给错了吧？