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[wolf0000 (lockingwolf)]

An urn contains N balls, identical in every respect except that they carry
numbers(1,2,...,N)and M of them are colored red, the remaining(N-M)white,0<M<N.
We draw a ball from the urn blindfolded, observe and record its color, lay
it aside, and repeat the process until n balls has been drawn,0<=n<=N.

(a)Find the probability of red on the first r consecutive draws in a specified
order.

為什麼書上答案是(1/N)(1/N-1)....(1/N-(r-1))???

而不是(M/N)((M-1)/(N-1))...((M-(r-1)/(N-(r-1))?
我翻了其它的書答案都是下者。

但我問了原書作者他說答案是(1/N)(1/N-1)....(1/N-(r-1))沒錯
他說是我英文翻錯才會算出(M/N)...這個答案
那到底是要怎麼翻?
不是說連續抽到r個紅球的機率嗎...???
那為什麼不是N個球中從M個紅球中取一個 * N-1個球中從M-1個紅球中取1*....
(樹狀圖分析)
而是(1/N)(1/N-1)....(1/N-(r-1))..........想不透~"~



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→ wolf0000:剛悟出了..是因為有規定要照特定順序，而每顆球用有編號
→ wolf0000:所以每次取一顆紅球都只有一種結果...0.0