Problem Solving

试题详情

题目：

Each of the integers from 0 to 9, inclusive, is written on a separate slip of blank paper and the 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 ?

选项:

A、Three
B、Four
C、Five
D、Six
E、Seven

答案:

E

提问：

点此查看答疑
May老师，这个真的一点思都没有呀[捂脸]
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提问：

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想问问老师7是怎么算出来的呀？这题是要用排列组合计算方法算吗？
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