The classical problem of eliminating a false coin out of 12 given can be solved using three steps of weighing by a simple level-balance, even without prior knowledge of the false coin being heavier or lighter than the standard coins.

Solve the same problem for 13 coins (i.e. 12 normal, one false , 3 steps to establish which is the different one and whether it is lighter or heavier), provided you may use a balance-scale with non-equal arms.

(In reply to Almost solution. by Jer)

Try arms with 2:1 length ratio, 3 coins will balance 6 if none is false etc

Posted by Ady TZIDON on 2011-02-18 04:40:28