紧急求助．我的 一道难题

dabenzhuzhu

各位好,我想请教l两道有关PREP方差的题希望哪位好心人帮忙讲解一下其祥解的过程:

１０６：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?

<A> 12.0  <B> 13.5 <c>17.0 <D> 23.5 <E> 26.5

110.
                11364-!-item-!-187;#058&007646

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

万分感谢．我２５日就考试了，学文科的我，数学差得一踏糊涂，不知道花了多少时间，但是仍然没有起色，我该怎么办呢，ＸＤＪＭ？

wei_wangyan

到数学JJ区问一下吧。