11 coins are indistinguishable by sight
Source: Russian 2007
September 6, 2007
countingdistinguishabilitycombinatorics proposedcombinatorics
Problem Statement
There are coins, which are indistinguishable by sight. Nevertheless, among them there are geniune coins ( of weight g each) and one counterfeit (of weight g). You have a two-pan scale which is blanced when the weight in the left-hand pan is twice as much as the weight in the right-hand one. Using this scale only, find the false coin by three weighings.