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發表於 2012-5-10 09:17:34
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B. 1/3
There are 2 cases:
Case 1. If you pick a black ball, the other ball is either a black, white or white ball (1/3 of getting a black ball)
Case 2. If you pick a white ball, the other ball is either a white, black or black ball (1/3 of getting a white ball)
The cases are indepedent and you have 1/2 of getting one of the cases (1/2 of the balls are white and the other half are black), so the chance is (1/2 x 1/3) + (1/2 x 1/3) = 1/3
Some brothers say you pick two balls out at the same time so it's 1/2, but keep in mind you only look at one ball first and not both of them at the same time, so it's 1/3 instead of 1/2. |
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樓主: oldcake
我喜歡九搭八!!
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在線雷達
發表於 2012-5-10 10:34:04
(不過有位師兄覺得禾個答案係錯架
) 
B. 三份一 (1/3) 
