need help for probability Q

2010-05-25 5:34 am

suppose there are three Urns each containing millions of poker chips. One of the urns (urn Red) contains 80% red chips and 20% blue chips. the other two urns (Urn Blue1 adn Urn Blue 2) each contain 80% blue chips and 20% red chips.

An urn is selected at random and five (5) chips are randomly drawn from that urn. It is observed that three(3) of the chips are red and the other two(2) are blue.

Question
1. what is the probability that the observation was made given that the balls were drawn from Urn Red?
2. what is the probability that the observation was made from given that the balls were drawn from either of the Urns Blue?
3. what is the probability that the sample was drawn from Urn Red?

更新1:

would u explain more of the Q3. not really understand how the numbers come from.

回答 (1)

用戶9112

2010-05-25 6:45 am

✔ 最佳答案

Please see the following:

圖片參考：http://img138.imageshack.us/img138/8383/38372428.png

2010-05-24 22:45:58 補充：
http://img138.imageshack.us/img138/8383/38372428.png

2010-05-25 20:20:08 補充：
Probability of the red urn is chosen = 1/3
Probability of red urn chosen and then 3 red chips and 2 blue chips drawn
= (1/3)(0.2048)
Likewise for blue urn and 3 red chips and 2 blue chips = (1/3)(0.0512)

2010-05-25 20:20:12 補充：
Total probability of 3 red chips and 2 blue chips
= (1/3)(0.2048) + (1/3)(0.0512) + (1/3)(0.0512)
Out of these only (1/3)(0.2048) is for red urn, hence the quotient

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