[中译] Puzzleup 2014 (7) Numbered Cards

楼主: LPH66 (-6.2598534e+18f)   2014-09-10 21:54:31
题目网址: http://www.puzzleup.com/2014/
http://www.puzzleup.com/2014/puzzle/?248
答题时限: 9月11日7PM-比赛结束(约12月17日)
加分时限: 9月11日7PM-9月17日6:59PM
答对可得基本分100分。答案可上传5次,每改1次答案从基本分扣20分。 
比赛期间内可随时上传答案,加分时限内答对第n天加(6-n)分       
另依题目的难易有额外加分(如有80%的人这题答错,答对者加80分)  
◆Numbered Cards
There are three boxes each containing some numbered cards. First box contains
three cards numbered as 1, 2, and 3. Second box contains four cards: 1, 2, 3,
and 4, and the third card contains five cards: 1, 2 ,3, 4, and 5. You will
randomly select a box and without seeing the inside you will randomly draw
two cards at the same time. If one of the cards is 4, what is the probability
that the other card is 3?
Enter your answer as a simplified fraction. Example:12/23
有三个盒子,内有数张写有数字的卡。
盒子内容如下:第一个盒子内有三张卡,分别写上 1, 2, 3;
第二个盒子内有四张卡,分别写上 1, 2, 3, 4;
第三个盒子内有五张卡,分别写上 1, 2, 3, 4, 5。
现随机选一盒子,并在不看盒子内容的状况下随机同时抽出两张卡。
若其中一张为 4,则另一张为 3 的机率为何?
答案以最简分数输入,如 12/23。
楼主: LPH66 (-6.2598534e+18f)   2014-09-10 21:54:00
经典条件机率题...

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