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gwd7-14

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楼主
发表于 2004-6-27 13:30:00 | 显示全部楼层

gwd7-14


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 ?


我做出来是1/3,答案是2/5,请帮帮忙!


我觉得加起来等于八,只有2和6,3和5,4和4三种组合,所以是1/3!

沙发
 楼主| 发表于 2004-6-27 19:08:00 | 显示全部楼层

谢谢tianwan,总是你回答我的问题,非常感谢!

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