Experience Points

Experience points are a measurement for how your character is progressing. The player character can earn experience points for killing creatures and solving quests. They are used to determine when a character should gain a new level.

Fallout 3
The experience points required for level N can be calculated from this equation: exp = 25(3N + 2)(N - 1) for lvl 20 save just before you get to it then complet it then load to the save just before you reached it and change your karma lvl then get to lvl 20 this way you can get all 3 for lvl 20 this also works for others (at least for me)