作者Ocanna (....)
看板GMAT
标题[计量] OG绿本PS 70
时间Mon Oct 12 18:03:30 2009
题目
If a certain sample of a 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
看了他後面的详解解释是
The value must be more than 2.5 standard deviation
above the mean or below the mean.
2.5*3=7.5
20-7.5=12.5
20+7.5=27.5
The only value outside the range of 12.5 to 27.5 is 12.0
so the answer is A
看了详解後还是无法理解他题目的要问的东西,
烦请高手板友们解惑(解释题目要问的东西最後一句~"~)
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1F：推 DreamKite:简单的留给下面高手抢答! 10/12 18:28
2F：推 stephanini:我觉得你可能只是不知道2.5SD是啥吧,就是2.5倍的SD 10/12 18:35
3F：→ Ocanna:2.5SD这个我懂,但我不懂为何要求那个范围? 10/12 18:38
4F：→ Ocanna:应该是我不懂from the mean的意思= =a 10/12 18:40
5F：→ stephanini:以下哪个数是从mean开始算,高於2.5SD或低於2.5SD 10/12 18:51
6F：→ Ocanna:我懂了..感谢~ 10/12 18:56