Insight · ★★★☆☆ · ~6 min
Crazy Postman
A postman delivers letters at random — expected number in the right house?
by MindYourPuzzle
A postman puts 1 letter in each of 2 boxes, then places each subsequent letter in a box with probability proportional to how many letters it already contains.
What is the expected number of letters in the smaller box after N total letters?
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