[中譯] Puzzleup 2012 (16) Faulty Product

[LPH66 (杇瑣)]

題目網址: http://www.puzzleup.com/2012/?home
          http://www.puzzleup.com/2012/puzzle/?257
答題時限: 11月８日７ＰＭ－比賽結束（約１２月１２日）
加分時限: 11月８日７ＰＭ－11月13日６：５９ＰＭ

答對可得基本分１００分。答案可上傳５次，每改１次答案從基本分扣２０分。
另有兩種加分： １. 加分時限內答對。例：第Ｎ天答對，可加（６－Ｎ）分。 
２. 題目越困難，加分越多。例：這題有ｎ％的人答錯，答對者加ｎ分。      

◆Faulty Product

In a factory every 5 products out of 100 are faulty. Samples from a randomly
selected product are sent to two different labs for testing. Labs have an
accuracy of 75%, and 90% respectively. If both of the labs report the product
is faulty, what is the probability that it really is?

Note: The probability of a lab reporting a faulty product as faulty and a
faultless product as faultless are both equal to the accuracy of the lab.

Enter your answer as a simplified fraction. Example:12/23

一個工廠裡每一百個成品就有五個不良。
現隨機抽樣成品送給兩個不同的實驗室測試。兩個實驗室的準確率分別是 75% 及 90%。
若兩實驗室皆回報不良，則它真的不良的機率是？

註：實驗室回報不良品為不良品的機率及回報良品為良品的機率皆為其準確率。

將答案以最簡分數表示，例如 12/23。

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基本分來了 (茶)

--
LPH  [acronym]
= Let Program Heal us
                        -- New Uncyclopedian Dictionary, Minmei Publishing Co.

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※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 180.218.108.125
※ 編輯: LPH66           來自: 180.218.108.125      (11/07 23:50)
推 Django:真的蠻基本的0.0
推 newacc:這感覺像是某種高中數學競賽的題目XD
推 walkwall:這不是Puzzleup  這不是Puzzleup  (遮臉)
※ 編輯: LPH66           來自: 180.218.108.125      (11/08 09:00)
推 Django:比較像課本練習題吧 XD 數學競賽出這個有點...
推 lollygagger:75%準度實在不高，95%的良品有1/4會驗成不良呢