GWD math 15 q2 真的搞不懂

guoqiongjiu · 发表于 2010-11-20 23:14:46

Q2:
A certain characteristic in a large population has a distribution that is symmetric about the mean m. If 68 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m + d ?

A.   16%
B.   32%
C.   48%
D.   84%
E.   92%

谢谢各位了

seyouji · 发表于 2010-11-20 23:20:30

画个图就出来了

guoqiongjiu · 发表于 2010-11-20 23:38:16

的确画了，可是没搞明白，能给解释下吗

zyzfrank · 发表于 2010-11-21 00:06:06

是D吗？

guoqiongjiu · 发表于 2010-11-21 00:15:48

是D吗？

-- by 会员 zyzfrank (2010/11/21 0:06:06)

是的，给我解释一下吧

zyzfrank · 发表于 2010-11-21 00:24:49

68%在平均值1个标准差之内也就是说68%的在【m-d，m+d】
由于是均衡分布所以【m，m+d】有68%/2=34%
m是均值小于m有50% 于是小于m+d的就有34+50=84%

matthewliu1981 · 发表于 2010-11-21 00:26:59

The total percentage of distribution for any values outside ( m-d, m+d) should be 100%- 68%=32%

Due to the nature of symmetry, the percentage of distribution for less than (m-d) or more than (m+d) should be equal. This leaves the percentage for any values more than (m+d) to be 32/2=16%. Since the total is 100%, the percentage for any values less than (m+d) should be 100%-16% = 84%.

GWD math 15 q2 真的搞不懂

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