Math puzzles!

Going back to this one, cause it bothered me that nobody solved it this way...
For each correct die, you win $1.
so 1/6*$1 + 1/6*$1 + 1/6*$1 = $0.50 per game
But: If none of the dice are right, you lose $1
so 5/6*5/6*5/6*$-1 = 125/216*$-1 = $-0.5787 per game
Add them up: $-0.0787 per game, or $0.9213 return on $1 investment.

Quite the nice solution to that problem