Can someone explain me how magic resistance works?

Can someone explain me how magic resist scales in WOTLK, and is it worth to take flask of lesser resistance on LK instead of hp coz lk deals huge dmg on soul ripper,and similar magic dmg situations like syndra.

I doubt its worth to use that flask, but there are other ways to reach[with minor sacrifices] certain resistance caps for great reliability on few specific encounters. Also resistance is quite "backseat" mechanic in wotlk, since any magic damage that's dangerous you can manage with defencives.

https://web.archive.org/web/20120329...chanics_wotlk/

Its kind of confusing to explain.
4 Resistance=1% Chance to Resist if your attacker is Level 80. (Raid Bosses are 83 and this is reduced to 0.75 I believe but I am not 100% sure.)
Alternatively, your Damage reduction is based on your percent to resist but your reduction only occurs in increments of 10%.

So for example, if you 205 Resistance you have 51.25% Chance to Resist. This gives you a chance to reduce DMG by 50% and a small chance to reduce DMG by 60%. Your DMG reduction will always be in an increment of 10%.

If you have 205 Resistance, and your Attacker is lvl 83, it will reduce your chance to resist from 51.25% down to 38.4% but your DMG reduction will still be 50%.

So alternatively, Less Resistance Flask will give you 12.5% (or 9.3% against Raid Boss) chance to resist and a 10% Damage reduction, which in my opinion, is much more valuable than 1300 HP.

If your Attacker is level 80-
100 Resistance is 25% chance to Resist and a 20% or 30% DMG Reduction
200 Resistance is 50% chance to Resist and a 50% or 60% DMG Reduction
300 Resistance is 75% chance to Resist and a 70% or 80% DMG Reduction
400 Resistance is 100% chance to Resist and a 100% DMG Reduction

This also only applies to PvE. The conversion formula is different for PvP.

Again, I'm not 100% sure thats how it works but thats how I understand it.