Source: 2010 Euler math Olympiad in Russia to Eighth graders. The author of the problem is Alexander Shapovalov
Problem: 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?
By the way, ten eighth grade students in Russia solved this problem during the competition. :P
Best of Luck! I am sure solving this problem will make you happy :)
Solution: Posted by Nikhil in comments!