This question already has an answer here:
You are in hell for all eternity and the devil gives you two dollar bills every day with increasing serial numbers. He then takes the dollar bill you have with the smallest serial number. At the end of your infinite stay in hell, do you have infinite money or no money?
The intuitive answer for me was that if you look at the partial sums, on the Nth day you'll have $N$ dollars. So clearly after infinity days you should have infinity dollars.
On the other hand, you can also prove that for every dollar you ever received, there's a corresponding day that the devil takes it back, leaving you with nothing in the end.
Which one is the right answer?