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
我知道因为只有2,6 3,5 4,4三种组合 所以概率一定是大于1/6 X 2=1/3的 但是D,E就不知道怎么推理了. 答案D.
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发表于 2010-1-23 03:26:59
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