Re: [童年] 殘念的99分
前略
※ [本文轉錄自 StupidClown 看板 #1DgwVLP2 ]
作者: hirabbitt (兔子) 看板: StupidClown
標題: Re: [童年] 殘念的99分
時間: Mon Apr 18 10:54:10 2011
中學的時候也碰到一個天才老師
一直堅持"機率=特定事件數/所有事件數"
題目好像是
"兩球隊比賽,A隊必須贏3場才算獲勝,B隊贏2場就算獲勝,
若兩隊贏球機率相同則A隊獲勝的機率是?"
老師答案:4/10
我們答案:5/16
老師:A球隊獲勝事件={AAA,AABA,ABAA,BAAA}四種
全部事件={AAA,AABA,AABB,ABAA,ABAB,ABB,BAAA,BAAB,BAB,BB}十種
所以是4/10
...全班還分成兩派戰了起來
我這邊只有我和蛇同學
更悽慘的是另一邊有一位我認為他數學很強的同學
...
課本上是有"機率=特定事件數/所有事件數"這一句啦
不過是放在前面的章節"所有事件機率相等"的情況下討論
而這題光是A球隊獲勝的四個事件={AAA,AABA,ABAA,BAAA}
機率就已經不相等了...
...
有這種老師
學生被教笨也不意外
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◆ From: 220.136.180.244
※ 編輯: hirabbitt 來自: 220.136.180.244 (04/18 10:55)
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完整的事件表
AAAA\___簡稱為AAA事件 機率為0.5^3
AAAB/
AABA 機率為0.5^4
AABB 機率為0.5^4
ABAA 機率為0.5^4
ABAB 機率為0.5^4
ABBA\___簡稱為ABB事件 機率為0.5^3
ABBB/
BAAA 機率為0.5^4
BAAB 機率為0.5^4
BABA\___簡稱為BAB事件 機率為0.5^3
BABB/
BBAA\
BBAB ___簡稱為BB事件 機率為0.5^2
BBBA
BBBB/
以上每個完整事件都是1/16的機率
但簡稱的事件部份機率各不相同
所以不能使用那個公式
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{AAA,AABA,ABAA,BAAA}
----------------------------------------------
{AAA,AABA,AABB,ABAA,ABAB,ABB,BAAA,BAAB,BAB,BB}
1/8+1/16+1/16+1/16
=---------------------------------------------
1/8+1/16+1/16+1/16+1/16+1/8+1/16+1/16+1/8+1/4
=5/16
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※ 編輯: hirabbitt 來自: 220.136.180.244 (04/18 12:59)
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◤ __ \__◣ ◢◤◢◤ ψhirabbitt
◢ ◤ ◢███◣ ◢███◣
我不是m █████ █████ 我不是s
██●█● █▇███
是溫柔 ██╱╲ ●◥█████◣● 是傲嬌
◥╱█╱╱ ● ◥████ ˇ
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◆ From: 220.136.180.244
※ 編輯: hirabbitt 來自: 220.136.180.244 (04/18 13:10)
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