TOT 246 1990 Spring O J4 counterfeit 2 of 61coins
Source:
March 12, 2021
combinatoricsweighings
Problem Statement
A set of coins that look alike is given. Two coins (whose weights are equal) are counterfeit. The other (genuine) coins also have the same weight, but a different weight from that of the counterfeit coins. However it is not known whether it is the genuine coins or the counterfeit coins which are heavier. How can this question be resolved by three weighings on the one balance? (It is not required to separate the counterfeit coins from the genuine ones.)(D. Fomin, Leningrad)