Some people here are arguing i think because the question asks an irrelavant outcome. The inital chance was 50/50. With the look at the 100 dollar bill your chances grew slightly to 2/3. But if you can't change the outcome of the game you still have a 50/50 chance at "winning". All you get is information which you can't use to change the outcome. So theoreticaly the Boxes will be choosen 50/50 but after you see a hundered dollars you can just slightly hope a little more easily. I think this is the reason why it's complicated your choice has a 50/50 chance and when you can't change it, it doesn't change. Your brain calculating chances can get a little bit happy but nothing more nowing it has 2/3 chance of winning.