1/N=2/K=2 1/K
因为1/K=1/K 1/
所以 2/K=2 =2
15. There are six cards each with a number from 1 to 6. Draw one card randomly and then put it back into a bowl. If one card is to be drawn randomly, and the sum of two cards is 8, whats the probability that the card is 5?
【答案】2/5
【思路】因放回,两张cards之和=8有5种可能,2 6,6 2,3 5,5 3,4 4,其中出现5的可能有2种。
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