[GMontag]

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Didn't read the whole thread, but personally I pick $99. I expect this performs the best against the field of 'random people picking'.

I gain $0 instead of $2 against perfectly rational Nash-equilibrists, but gain $101 against GMontag and others. This seems like a good strategy as I expect there are more of the latter than the former.

Surely no-one can justify picking $100, a number which *always* does worse than picking $99 - no matter what number the opponent picked. I just cannot imagine any credible explanation for $100. Every other number makes sense in that it can do well against opponents with a certain range, but $100 can never be correct.

I also assume that everyone who picked $100 would also choose 'keep silent' in the prisoner's dilemma, even though it's a dominated strategy?

Would be interesting to hear the justification of anyone who would pick $100 here, but choose 'Betray' in prisoner's dilemma.

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The justification depends on the opponent. In this situation, the problem stipulates "infinite" rationality (i.e. I know he's rational, he knows I know he's rational, I know he knows I know he's rational, ad infinitum) for both players. The normal formulation of the Prisioner's Dilemma doesn't make such a stipulation. If it did, the correct answer there would also be to keep silent.