Apparently with 260 MR you take more than 70% reduced magic damage.
And I ask each and every one of you,do you really find it healthy?
That's the reason tanks are overpowered,you see it's not 260 flat magic resist,that number scales up to a percentage and I believe it maxes out at 74% ?
That's why they are fking unkillable,thay have 4000hp,enough base damage to fuck you up (and for some reason they even have strong scalings too) AND on top of that a lot of cc,low cooldowns and they are not skill based champions and they are running around getting 70% reduced magic damage,or arrouns 50% of you have a void staff?
Come on guys that's ridiculous,I understand that they are tanks but in many games they don't fuck you up..they are just hard to kill and have tons of cc,why in league of legends they have so much base damage and scalings too?
I made this post because I just realised after reading the little letters that appear when you hover your cursor on the armor or the magic resist of a player there is a % damage reduction that all this time I thought was simply a flat damage reduction,for example you have 250 armor you block 250 ad damage, not being immune to 70% ad damage..
or something and 
, the highest MR item numbers are 80 from stoneplate and i think 55 from other items, so your going to need a lot of items in just MR.
and the only common MR bonuses that are at a spammable level would probably be 
giving 30 on shield 
givingup to 30%
getting 15%-30% depending on HP,lasting forever though.as well as 
giving him and another entity 16% of his armor
ARMOR HOWEVER
is debatable. ADC do a lot of damage, and there are ADCs like 
with some extra damage of another type
they also come in higher numbers like 80 and 100 
and higher multipliers.
is at 20% but its at all times and it goes on somebody else too
and 
have a 90% buff which can go up to 109% bonus armor, the conditions being ramus is using ball curl and malphite has his shield up both of which are on a 6 second CD
though something worth mentioning, is i have played 
with his AS passive up gets to .3 attack speed.