An example of using the exclusion-inclusion formula is the following matching problem. An absent-minded person (some authors prefer talking about a secre- tary) has to put n personal letters in n...

Extracted text: An example of using the exclusion-inclusion formula is the following matching problem. An absent-minded person (some authors prefer talking about a secre- tary) has to put n personal letters in n addressed envelopes, and he does it at random. What is the probability pm., that exactly m letters will be put correctly in their envelopes? Verify the limit lim Pmn= em!