Talk:Last Whisper/@comment-96.251.91.14-20110922011049/@comment-4068613-20111105203221

% armor and MR pen ignore a % of the enemy's armor before applying flat penetration. So if your opponent has 100 armor, this is like 40 armor pen, applied before your flat pen. So if you have this and 20 flat armor pen against an enemy with 100 armor, you ignore 40 of it by the % pen, and then you ignore 20 more by the flat pen, allowing you to hit as though they had 40 armor isntead of 100.