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 re: question for Kenny by Kenny M)

Along the same lines of an original RF vs RF, what if the next weighing had those four: RRFF against, say RRRF.  The heavy side is not all R; you might choose the F.

Posted by Charlie on 2013-10-19 01:38:08