A typist types four envelopes and four letters. She places the letters in the en

游客2023-10-16  22

问题 A typist types four envelopes and four letters. She places the letters in the envelopes at random. What are the chances that only three letters are in their correct envelopes?

选项

答案 zero

解析 (如果三个都装对了,那么第四个也一定装对了,所以没有这种几率。)  
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