[求助]一道数学题

rosemarys

[求助]一道数学题，是在考条件概率么？

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?

A. 1/6

b. 1/5

c. 1/3

d. 2/5

e. 2/3

这题是在考联合概率吧，我不知道该如何解这个题，一碰到联合概率，我就晕了。请大家帮忙给解答一下，谢谢！

rosemarys

答案是D

dbearwangs

the sum of the numbers on the cards is 8: 4,4; 5,3; 3,5; 6,2; 2,6

one of the two cards drawn is numbered 5: 5,3; 3,5

so 2/5