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标题: 请大家帮我解答一下这道题，谢谢 [打印本页]

作者: usagmat 时间: 2009-5-11 07:09 标题: 请大家帮我解答一下这道题，谢谢

Each of the intergers from 0 to 9, inclusive, is written on a separate slip of blank paper and ten slips are dropped into a hat. If the slips are then drawn one at a time without replacement, how many must be drawn to ensure that the numbers on two of the slips drawn will have a sum of 10?

A. 3

B. 4

C. 5

D. 6

E. 7

谢谢。正确答案为什么是E。

作者: tomrchu 时间: 2009-5-11 19:40

pay attention to "ensure", so that means "must have sum of 10", so you have to draw: 0,1,2,3,4,5,6. since even when you reach 5, the biggest sum is still 9. so you have to draw anther one, which is "6"

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