Q14:
Six cards numbered from 1 to 6 are placed in an empty bowl.  First one card is drawn and then put back into the bowl; then a second card is drawn.  If the cards are drawn at random and if the sum of the numbers on the cards is 8, what is the probability that one of the two cards drawn is numbered 5 ?

概率可以通过probable outcomes / sample space
可能出现的组合有：2+6，3+5，4+4，5+3，6+2：共5种（而且random，所以每一种的概率也都一样）
其中2种是带有5的
所以，2/5

通过概率的算法是：
A：和为8的概率
B：出现5的概率
求得是p(A|B)
P(B|A)=P(B and A) / P(A)
P(A)= 5/36
P(B and A)= 2/36
=> P(B|A)=2/5

引用:

原帖由 chinatubie 于 2006-3-31 06:15 发表
通过概率的算法是：
A：和为8的概率
B：出现5的概率
求得是p(A|B)
P(B|A)=P(B and A) / P(A)
P(A)= 5/36
P(B and A)= 2/36
=> P(B|A)=2/5

谢谢土鳖！