很挑战的两道数学题,你会吗?

dabenzhuzhu

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.
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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．

qhma

A,D

prayer

我的答案是DC啊，唉，不知道对不对，和ls没一个一样的。

书上说deviation standard越小，与mean离散越小，根本不用计算的嘛，找个最接近mean的

wandola

其实这样的distribution的问题是灰常灰常简单的。

1. Mean=20, STD=3, the value is more than 2.5STD away from mean --> the range of the values is thus: value<20-3*2.5=12.5; or value > 20+3*2.5=27.5;

2. By the same token ... (heehee...i am preparing AWA now...)

value is thus in the range:   21-2*6<value<21-1*6; or 21+6<value<21+2*6

chonheinrich

LS正解，不要想太多

好象绿皮OG上有原题还是差不多的题目的，看看讲解吧

dabenzhuzhu

太感谢了,我25日就要考试.祝福我好运吧.

chonheinrich

祝福你好运！

dabenzhuzhu

谢谢,考试后我一定奉上机经.