作者lai90043 (賴伯)
看板Grad-ProbAsk
標題[理工] [機率] 排列組合
時間Tue Sep 27 22:49:38 2011
there are three types of animals in a laboratory:15 type I
13 type II &12 type III.Animals of type I react to a particlar
stimulus in 5 sec ,type II and type III react to the same
stimulue in 4.5 sec and 6.2 sec, respectively.A psychologist
selects 10 of these animals at random and finds the a exactly
four of them react to this stimulus in 6.2 sec.What is the
prob that at least two of them react to the same stimulus
in 4.5 sec.
我的想法是
B = 至少兩隻type II
A = 十隻有四隻type III
_
P(B│A) = 1 - P(B│A)
12 13 15 12 15
P C C + P C
4 1 5 4 6
=1 - ──────── * 6! (請問這樣列有錯嗎?)
40
P
10
Ans: 0.8831(我跟算的跟答案不一樣 我不知道是我哪列錯 還是計算機按錯?)
===========================================================================
12 13 15 12 15
C C C + C C
4 1 5 4 6
=1 - ───────── 不考慮順序的話 改成這樣 也跟答案不同
40 為什麼??
C
10
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 220.129.38.177
推 vanillaXleft:答案是哪個@@ 09/27 23:00
→ lai90043:0.8831 09/27 23:08
※ 編輯: lai90043 來自: 220.129.38.177 (09/27 23:10)
→ vanillaXleft:1 - (15C6+15C5*13C1)/(28C6) 09/28 00:18
→ vanillaXleft:我算也是 0.8831 @@ 09/28 00:19
推 KAINTS:P(至少兩隻TYPEII|有四隻TYPEIII)= 09/28 01:41
→ KAINTS:P(至少兩隻TYPEII|六隻TYPEI or TYPEII)= 09/28 01:42
→ KAINTS:1-(13C1*15C5+13C0*15C6)/28C6=0.8831 09/28 01:44
→ KAINTS:這題沒有順序 所以都用組合數就可以了 09/28 01:45
→ lai90043:樓上那是課本的解法吧 我想問的是 我列式錯在哪裡了? 09/28 08:45
※ 編輯: lai90043 來自: 220.129.35.110 (09/28 09:26)
→ KAINTS:條件機率樣本空間會改變 妳那樣列的意思是從10挑出 09/28 11:29
→ KAINTS:與題目意思不同 09/28 11:32
→ lai90043:想通了 謝謝 09/30 23:27