Rohit said:
how about something a little harder? this one is easy. you weight 6 on one side 6 on the other, which ever is the lightest you dump those 6 out then split the remaining 6 into 2 groups of 3, again look for the lightest and dump that one out. now your left with 3 so u measure 2 of the 3 if they r the same weight then you know the 3rd ball is the one or if one is heavier then the other then you know that way as well
Yep, that's it. Now what if I were to tell you that there's more than one way? At least 5 more ways to do this. See if you can figure them out. (Your solution would be 6:3:1)
If you get bored, try 18 balls, using the scale again only 3 times.
And TZ, you can use put as many balls on any sides.