JJ 340

apple7912 · 发表于 2012-1-11 11:57:16

4个数s, t, u, v，下面哪组数的standard deviation跟它们一样？（s,t,u,v 就是字母，不是实际数）
1. |s|, |t|, |u|. |v|
2. 3s, 3t, 3u, 3v
3. s^3, t^3, u^3, v^3
4. 2s+2, 2t+2, 2u+2, 2v+2

1.2.4 应该不对，3？

我叫胖河线 · 发表于 2012-1-11 11:58:03

3也不对

hookem09 · 发表于 2012-1-11 12:01:50

I just posted in other thread, "standard deviation is basically the difference between each number. Say s t u v = 1, 2, 3, 4, the gap between each number is 1. If 3s, 3t, 3u, 3v, then 3, 6, 9, 12 and gap between each number increased to 3. The correct answer for number 4 is (|s|, |t|, |u|, |v|). Multiplication will increase the standard deviation "

apple7912 · 发表于 2012-1-11 12:04:58

绝对值那个啊？那如果数字有负的，绝对值不是把差距缩小了啊？

hookem09 · 发表于 2012-1-11 12:07:15

the absolute value doesn't matter, what matters for standard deviation is the difference between each number. if s t u v is -1, -2, -3, -4, the difference between each number is still 1. Changing them to |s|, |t|, |u|, |v|, then the difference between 1, 2, 3, 4 is still 1.

hookem09 · 发表于 2012-1-11 12:10:06

eeks you are right, i didnt consider two positive and two negatives. is this all the problem gave us?

otono · 发表于 2012-1-11 12:11:16

同求 up

hookem09 · 发表于 2012-1-11 12:11:25

I don't see why number 3 can be correct since the number 1^3 is still one.. maybe the right answer is none of them

神经质 · 发表于 2012-1-11 13:31:29

4个都不对
1、绝对值，会改变密度分布
2、3倍，则D也为3倍
3、3次方，就跟不对了，同样改变密度分布
4、2倍再加2，同2~~~
除非他给出具体的限定，不然这几个都不对

sendyhoney · 发表于 2012-1-11 19:26:04

我也觉得都不对 ><

JJ 340

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