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 question for Tristan by xdog)

You're right, I made a miscalculation.  It doesn't seem like there's a quick fix.

Posted by Tristan on 2013-10-20 00:37:09