Ive been wondering, since kayle passive shred 15% of their armor + the 8% of the masteries. if u stack these with last whisper and black cleaver it does 83% armor pen if stack plus u can reduce whats left with flat armor pen. i wanted to ask if can this be done?

im not used to posting so my posts are somewhat strange to read.

Well sure, but make sure you're bringing enough damage to go through the armor you've shredded =P Also be aware if your opponents are actually building enough armor for that much pen/shred to be worth it. If they're not, you benefit more from increased damage or AS.

No, it doesn't stack that much. Percentage reductions + penetration of armor are applied separately and thus stack multiplicatively.

All of those effects combined will reduce the enemy armor by 1-0.85*0.7*0.65*0.92 = 1-0.356 = 64.4%