Anyway, I knew a lot of things carried the name Bernoulli (Bernoulli principle, Bernoulli numbers, Bernoulli's equation, Bernoulli distribution...they ran a damn franchise), but I didn't know until researching today's problem that it wasn't just one really prolific guy, but rather a family affair. That made me feel a bit better about things.
This all relates because today's problem apparently was a favorite of Nicolaus Bernoulli (1695-1720), who I take it was the looker of the family:
So this lovely family invented a lot of tricky math stuff that helped us understand the world better, but made my sophomore year GPA suffer a bit more than was strictly necessary. So now dear reader, I will let them loose on you:
A correspondent writes seven letter and addresses seven envelopes, one for each letter. In how many ways can all of the letters be placed in wrong envelopes?