The following is a true situation that I faced and I was wondering if it is possible to roughly estimate the odds of it happening (like you sometime see rough estimations of "The odds of you winning the lottery are one to .....").
About 2 years ago, my 10 years old boy met his 10 years old friend. While they talked, they discovered that both of them took from the library the same book - "The never ending story" - and are reading it at the same time.
Since this book was mainly famous in the 80's and had no promotion / hype at the time of the scenario, there is no possibility that both of the kids got introduced to it by a common 3rd party.
I guess the odds are more complicated than "there are X books in the library, so the odds are 1 / X"
