A predetermined algorithm for detecting a counterfeit coin with a multi-arms balance Original Research Article

We consider the classical problem of searching a light coin in a set of n coins, n − 1 of which have the same weight. The weighing device is a balance scale with r ⩾ 2 pans that, when r equally sized subset of coins are weighted, indicates the eventual subset containing the light coin. We give a predetermined algorithm that requires the minimum possible average number of weighings for almost all values of n.