> >
> > > > You have twelve marbles and a balancing scale.
> > > >
> > > > You know that one of the marbles has a different
> > > > weight than the other eleven.
> > > >
> > > > Your job is to find this marble, and to find out if it's
> > > > heavier or lighter than the others.
> > > >
> > > > What's the minimum number of weighings required?
> > >
>
> It ain't that complicated.
> Put 6 on one side and 6 on the other.
> Put aside the light six and put 3 on one and 3 on the other. Put aside the light 3 and put one on one side and one on the other. If they are the same mass, the one in you hand is heavier. If they are different it's the one on the lower pan.
> I'm not very good at this kind of problem, but that one was easy. Got anything tougher?
> Howard


Another approach.
Put one marble on each of the pans and if one is heavier, you've found it in one move. Sure, its a long shot, but it could happen.
Howard