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IMO 1979 - Shortlisted problems Question 2

IMO Shortlist · IMO 1979 - Shortlisted problems

Question 2

(BEL 4) From a bag containing $5$ pairs of socks, each pair a different color, a random sample of $4$ single socks is drawn. Any complete pairs in the sample are discarded and replaced by a new pair draw from the bag. The process continues until the bag is empty or there are $4$ socks of different colors held outside the bag. What is the probability of the latter alternative?