Problem of the MONTH!

Ok guys, as promised here is Erickson's solution and the original Doomsday Scale POW:

• The Problem
• Erickson's Solution
  

If you can find another way to solve this problem, and type up your solution on your start.archimedes account you are still eligible for half the prize money, 150 Duffy Bucks!

The Problem of the Month is a simple extension on this problem. Instead of 20 bags, now you only have to deal with 12. However, you don't know if the phony bag is light or heavy! The scale is still the same and you only have three opportunities to use it. Remember, this is a very difficult problem, and so I am offering 1000 Duffy Bucks for well-written, clearly thought out, 1 page solutions. Good luck!