how would you answer this brainteaser?

[JTsyo]

The other person either got a $20 or $80. Let's say it's $80. If you got $160 you wouldn't ask for a trade, therefore you got $40. Assuming the other person is aware of this, he should reject your offer. Therefore there is no upside to offer to trade. Either you get rejected or might get downgraded to a $20.

this
10,20,40,80 or 160 you don't trade. assuming both think the other player will make the best choice.
5 you can try

 

[DaveSimmons]

A: The other guy has $80. If he has $80, he knows that you either have $40 or $160. Since only a moron would trade away $160 in a game like this, he's going to know you have $40. And, he will say, "no thanks."

This is the key, that there is a $160 maximum. If it was an infinite sequence then the expected value calculation of $50 (.5x $20 + .5x $80) would work. ($160 holder would try for $320, $320 holder would try for $640, ....)

I missed that, d'oh!

 

[DAPUNISHER]

Nnever bet against a sicilian when death is on the line!

Winnar!

 

[DrPizza]

Nnever bet against a sicilian when death is on the line!

lmao, that was going through my head as I was typing. And, before reading and editing my response - originally, I extended the logic all the way down to 5 dollars - it was even more convoluted.

And, I like the problem. I'm sticking it on my next tests as an extra credit (along with the word, "explain.")

 

[DaveSimmons]

Just be kind and consider giving people like me who stop at the expected value partial credit

 

[JTsyo]

lmao, that was going through my head as I was typing. And, before reading and editing my response - originally, I extended the logic all the way down to 5 dollars - it was even more convoluted.

And, I like the problem. I'm sticking it on my next tests as an extra credit (along with the word, "explain.")

logic is the same for all the other amounts.