Yes, it wasn't all that hard, but I did spend hours on it. Sorry you didn't get the joy out of it. Beyond simply finding a solution (by the way, the version I was first given also required determination of which way the counterfeit coin leaned - light or heavy,) its an interesting problem in that it admits a few rather different approaches.
My current favorite (which I did not discover on my own) discovered here under "Communication Theory Analysis".
