Among 100 coins exactly 4 are fake. All genuine coins weigh the same; all fake coins, too. A fake coin is lighter than a genuine coin.
How would we find at least one genuine coin using two weighings on a balance scale?
Source: 2010 Euler math Olympiad in Russia- authored by A.Shapovalov
(In reply to Solution
That doesn't quite work. Say that the first weighing balances, and 12 are LL. Then suppose that coins 34 are NN. 12< 34, but there's still an L somewhere in the pile of 47 coins.
Interesting puzzle, will think about it.
Posted by Tristan
on 2013-10-19 03:38:57