As spiral suggested, i will post this question:
"Spiral was putting n letters into n envelopes and sent them off. However, Spiral not being the brighest
was unsure if he sent them to the right address. Prove the probability that at least one letter went to
the right address is given by :
"Spiral was putting n letters into n envelopes and sent them off. However, Spiral not being the brighest
was unsure if he sent them to the right address. Prove the probability that at least one letter went to
the right address is given by :