[中學] 不同樣本空間的 X 為何期望值會相等?
一袋中有 2 白球 8 紅球,今從袋中取球,求取得白球個數之期望值
1) 一次取出三球 => 期望值 = 3/5
2) 一次取一球,取後放回,取三次 => 期望值 = 3/5
3) 一次取一球,取後不放回,取三次 => 期望值 = 3/5
所以這種題型還可以衍生出速解,
算取一次的期望值 (= 1/5) 再乘以 3 就是答案。
請問為何會這麼巧呢? 三個我按基本定義都算過一次答案的確都是 3/5,但是
1) 的樣本空間元素有 C(10,3) 個
2) 的樣本空間元素有 10^3 個
3) 的樣本空間元素有 10*9*8 個
這三者之間有什麼定理或直觀可以連結所以才會相同?
--
--
※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 111.255.68.109
※ 文章網址: http://www.ptt.cc/bbs/Math/M.1400012344.A.A7F.html
→
05/14 04:22, , 1F
05/14 04:22, 1F
→
05/14 05:13, , 2F
05/14 05:13, 2F
→
05/14 05:14, , 3F
05/14 05:14, 3F
→
05/14 05:15, , 4F
05/14 05:15, 4F
→
05/14 05:16, , 5F
05/14 05:16, 5F
→
05/14 05:16, , 6F
05/14 05:16, 6F
推
05/14 07:51, , 7F
05/14 07:51, 7F
→
05/14 10:55, , 8F
05/14 10:55, 8F
→
05/14 10:56, , 9F
05/14 10:56, 9F
→
05/14 10:57, , 10F
05/14 10:57, 10F
→
05/14 10:58, , 11F
05/14 10:58, 11F
→
05/14 10:58, , 12F
05/14 10:58, 12F
→
05/14 10:59, , 13F
05/14 10:59, 13F
→
05/14 11:00, , 14F
05/14 11:00, 14F
→
05/14 11:00, , 15F
05/14 11:00, 15F
→
05/14 14:48, , 16F
05/14 14:48, 16F
→
05/14 17:37, , 17F
05/14 17:37, 17F
→
05/14 17:38, , 18F
05/14 17:38, 18F
→
05/14 17:38, , 19F
05/14 17:38, 19F
→
05/14 17:40, , 20F
05/14 17:40, 20F
→
05/14 17:40, , 21F
05/14 17:40, 21F
→
05/14 17:41, , 22F
05/14 17:41, 22F
→
05/14 17:41, , 23F
05/14 17:41, 23F
→
05/14 17:42, , 24F
05/14 17:42, 24F
→
05/14 17:42, , 25F
05/14 17:42, 25F
→
05/14 17:42, , 26F
05/14 17:42, 26F
→
05/14 17:46, , 27F
05/14 17:46, 27F
→
05/14 17:46, , 28F
05/14 17:46, 28F
→
05/14 17:48, , 29F
05/14 17:48, 29F
→
05/14 17:48, , 30F
05/14 17:48, 30F
→
05/14 17:49, , 31F
05/14 17:49, 31F
→
05/14 17:50, , 32F
05/14 17:50, 32F
→
05/14 17:50, , 33F
05/14 17:50, 33F
→
05/14 17:51, , 34F
05/14 17:51, 34F
→
05/14 17:51, , 35F
05/14 17:51, 35F
→
05/14 17:51, , 36F
05/14 17:51, 36F
→
05/14 17:52, , 37F
05/14 17:52, 37F
→
05/14 17:54, , 38F
05/14 17:54, 38F
→
05/14 17:55, , 39F
05/14 17:55, 39F
→
05/14 17:55, , 40F
05/14 17:55, 40F
→
05/14 17:59, , 41F
05/14 17:59, 41F
→
05/14 17:59, , 42F
05/14 17:59, 42F
→
05/14 18:46, , 43F
05/14 18:46, 43F
→
05/15 12:28, , 44F
05/15 12:28, 44F
→
05/15 12:29, , 45F
05/15 12:29, 45F
→
05/15 12:30, , 46F
05/15 12:30, 46F
→
05/15 12:31, , 47F
05/15 12:31, 47F
→
05/15 12:32, , 48F
05/15 12:32, 48F
→
01/02 15:46,
5年前
, 49F
01/02 15:46, 49F
→
07/07 12:07,
4年前
, 50F
07/07 12:07, 50F