作者Ocanna (....)
看板GMAT
標題[計量] OG綠本PS 70
時間Mon Oct 12 18:03:30 2009
題目
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
看了他後面的詳解解釋是
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
看了詳解後還是無法理解他題目的要問的東西,
煩請高手板友們解惑(解釋題目要問的東西最後一句~"~)
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1F：推 DreamKite:簡單的留給下面高手搶答! 10/12 18:28
2F：推 stephanini:我覺得妳可能只是不知道2.5SD是啥吧,就是2.5倍的SD 10/12 18:35
3F：→ Ocanna:2.5SD這個我懂,但我不懂為何要求那個範圍? 10/12 18:38
4F：→ Ocanna:應該是我不懂from the mean的意思= =a 10/12 18:40
5F：→ stephanini:以下哪個數是從mean開始算,高於2.5SD或低於2.5SD 10/12 18:51
6F：→ Ocanna:我懂了..感謝~ 10/12 18:56