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9

Part of 2017 Moscow Mathematical Olympiad

Problems(1)

Detective interrogates

Source: Moscow Math Olympiad 2017, Grade 11, P9

4/25/2017
There are 8080 peoples, one of them is murderer, and other one is witness of crime. Every day detective interrogates some peoples from this group. Witness will says about crime only if murderer will not be in interrogatory with him. It is enough 1212 days to find murderer ?
combinatorics