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[Problem Solving]
试题详情
题目：
A certain online form requires a 2-digit code for the day of the month to be entered into one of its fields, such as 04 for the 4th day of the month. The code is valid if it is 01, 02, 03, ..., 31 and not valid otherwise. The transpose of a code xy is yx. For example, 40 is the transpose of 04. If N is the number of valid codes having a transpose that is not valid, what is the value of N ?
选项:
A、12
B、13
C、18
D、19
E、20
答案:
D
提问：
我觉得C为什么不可以选？
解答：
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提问：
我觉得C为什么不可以选？
解答：
点赞0
阅读1148
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