[NaobisDad]

thanks for the replies again guys. You'll have to bear with me, I'm no mathmatician or statistician (is that a word?) so I'm slow here.

@econ: high econ I don't know anything about priors, so I'll need some further explanations on that. You said:
"but the participant must have some belief about how likely different values of N are." and went on to describe how the value might influence the way in which he determines ev.
In the original post it is stated that:
"Argument 1: It's +EV to switch. You had a 50/50 chance of picking the high or low envelope so there's a 50% chance that the other envelope is the high and a 50% chance it's the low. Therefore, EV of switch = 0.5*(+100) + 0.5*(-50) = +25."
nowhere here do I read anything about how the size of the value influences the decision to switch. Rather, I read that upon learning the value, switching is EV.

@Phzon: you said: "I don't like the idea that explaining why always switching is equivalent to always not switching is a solution. It's not complete. As bigpooch mentioned in the other thread (and others have mentioned in past threads), you can do better than either always switching or always not switching."

I merely refer to the fact that argument 1 as stated implies that switching will always be positive EV upon learning the value. Argument 2 says it will never matter. You might be able to do better by sometimes switching, but imo that was not stated in the original problem. For that reason I simplified to always switching. Similar to my respons to Econ, choosing a switch strategy might well influence your EV, however as I understand it, that was not waht was stated in the original problem. Correct me if I'm wrong.

@Tom: Are you saying that the sampling method will unintentionally provide information on the value of envelope 2 and that in this manner the sampling method is significant to the problem?

Again, my question really comes down to it that my friend believes it's not a paradox, rather that argument 1 is based on a fallacy. How did he do? is he right?