标准方差不会做！！OTZ（已解答）

灵狩Icy

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

跪了。。。答案是D，求详解。

lululuna

21-6*1=15,
21-6*2=9
所以Pat看电视的时间范围在[9,15],只有D项符合标准。

灵狩Icy

lululuna 发表于 2015-5-12 09:17
21-6*1=15,
21-6*2=9
所以Pat看电视的时间范围在[9,15],只有D项符合标准。

还是没看懂，为啥用21-6*1？？

lululuna

灵狩Icy 发表于 2015-5-12 09:30
还是没看懂，为啥用21-6*1？？

翻译下题目： between 1 and 2 standard deviations below the mean

是说PAT看电视的时间，实在比算数平均数小1到2个标准差之间[X-σ,X-2σ],能理解吗？

灵狩Icy

lululuna 发表于 2015-5-12 09:40
翻译下题目： between 1 and 2 standard deviations below the mean

是说PAT看电视的时间，实在比算数平 ...

OTZ 我太渣了。。还是没懂。。。我还是放弃标准方差的题目吧。。我感觉连这个中文都看不懂。。。谢谢OTZ

灵狩Icy

lululuna 发表于 2015-5-12 09:40
翻译下题目： between 1 and 2 standard deviations below the mean

是说PAT看电视的时间，实在比算数平 ...

啊，我终于懂了！！谢谢！！
我已经把你的答案更新到我的主题帖~~里面还有2道题没答案~~求围观解答！！！
http://forum.chasedream.com/foru ... id=991168&page=