求救关于方差类型的题目··· 请NN讲解下 真的是一点也不会···

xyqirene

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 deviations from the mean?



(A) 12.0

(B) 13.5

(C) 17.0

(D) 23.5

(E) 26.5

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



For a certain examination, a score of 58 was 2 standard deviations below the mean, and a score of 98 was 3 standard deviations above the mean.What was the mean score for the examination?



(A) 74

(B) 76

(C) 78

(D) 80

(E) 82




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



For a certain examination, a score of 58 was 2 standard deviations below the mean, and a score of 98 was 3 standard deviations above the mean.What was the mean score for the examination?



(A) 74

(B) 76

(C) 78

(D) 80

(E) 82

joyce22

http://forum.chasedream.com/GMAT_Math/thread-332979-1-1.html?SearchText=方差类型

这里有详细讲解

小玛雅人

楼上的头像，超赞！

xyqirene

thx~~~