It is illustrative to show the kth draw's probability is a/(a+b).
Method 1: sample space S=(w1,w2,...wa;r1,r2,...rb),E=(w1,w2...wa) P(E)=C(E)/C(S)=a/a+b
Method 2: taking k balls means a permatation from P(a+b,k).The last is white, number is (a/(a+b))*P(a+b,k).So,P(E)=(a/(a+b))*P(a+b,k)/P(a+b,k)=a/a+b.
回複:回複:explain pls:)
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謝謝jinjing(進京考試?)。久仰你的大名,大俠!
-戲雨飛鷹-
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01/11/2010 postreply
09:47:29
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回複:謝謝jinjing(進京考試?)。久仰你的大名,大俠!
-jinjing-
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01/11/2010 postreply
11:01:38
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謝謝你,數學master:)
-戲雨飛鷹-
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01/11/2010 postreply
13:08:04
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對了,我還把你給的那個公式告訴了朋友:
-戲雨飛鷹-
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01/11/2010 postreply
09:51:15
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回複:對了,我還把你給的那個公式告訴了朋友:
-jinjing-
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01/11/2010 postreply
11:20:47
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thanks, jinjing.
-戲雨飛鷹-
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01/11/2010 postreply
13:06:29