You can take a 1/2 chance of winning 16 dollars, or a 1/3 chance of winning 81 dollars, or a 1/4 chance of winning 256 dollars, or a 1/5 chance of winning 625 dollars, etc. (1/x chance of winning x^4 dollars). Which do you choose?
I'd take the 20% chance. As its a tidier sum for -5% and any figure below $100 isn't really going to change anything worthwhile.
