请教一道prep数学题

gfhzmj

The residents of Town X participated in a survey to determine the number of hours per week each resident spent watching television. The distribution of the results of the survey had a mean of 21 hours and a standard deviation of 6 hours. The number of hours that Pat, a resident of Town X, watched television last week was between 1 and 2 standard deviations below the mean. Which of the following could be the number of hours that Pat watched television last week?

A 30
B 20
C 18
D 12
E 6

不理解题目说什么，哪位MMJJ解释下

scutpigus

意思是说调查显示X市的居民每周平均看电视21小时，标准差是6小时。其中PAT上周看电视的时间为小于平均时间的1-2标准差以内。

所以：21-6*2<X<21-6 答案为12小时

gfhzmj

原本以为是PAT的标准差在1到2之间。

现在懂了，3Q