有关置信区间的计算

题目

有关置信区间的计算
In a finance course at a business school,6 students are randomly selected.Their mean score on the final exam is 75,with standard deviation 8.
6个学生随机抽取出来,期末平均成绩是75,方差是8
What is the 95% confidence interval for the average class score on the final?
在95％的自信度下,全班的平均成绩是?
[66.6,83.4]
[67.6,82.4]
[68.6,81.4]
[71.7,78.3]
我的算法就是上限＝75＋1.96*8／根号6＝81.4
选c,但答案批我错,是不是答案错了?

答案

你是对的
z0.975=1.96
上限＝均值＋1.96*sigma／根号n