$336,300 for a retirement fund - not bad.
the game is very well done with pleasing visuals. I enjoyed coming up with a near perfect strategy, and would've probably continued to play if there were more levels!
Well done! :D
SPOILERS!
I think this is a foolproof way of beating each level
1) start with 55555
2) for - drop that number to 3 / for + increase it to 7
3a) If you now have -- for a number decrease to 1 / if you have ++, increase to 9
3b) Otherwise (ie if the cumulative result is -+ or +-) the number is between the digits you entered
4) Repeat until you have all the numbers