one is a counterfeit that looks identical to the other 11. Using a balance
scale and only three weighings, how would you determine which is the
counterfeit coin and whether it is heavier or lighter than the real coin ?
clues: How many stacks of coins will you use; how many coins per stack;
which coins will you test against each other in the 1st weighing; and which
ones in the 2nd weighing if the 1st weighing does or doesn't balance.
Congratulations to these solvers as of
Adam Albright-Hanna, Danny Blanco, Karl Cosner, John & Alex Durski,
Albert Frank, Tomasz Grabowski, Joshua Green, Bill Hosch, Steve Kobes,
Rabih Assem Kodeih, Napawong Leelaprechalert, LW Luk, Chris Magson,
Claire Weglarz and Andrey Zhuravlev.