Thing is with any percentage drop rates there is no guarantee you will get the drop at all. even if something had a 90% drop there is a 10% chance you will not get that drop it does not mean that every 100 kills 10 will produce x item or even 100 out of 1000 will drop it either
it's per kill there is a % of a chance the item will drop, but the rest of the % is the % chance of it not dropping per kill, every kill has the same % that is reset rather than it being out of so many kills
so if it's 90% drop killing 10 does not make that 100% chance after every kill it is still 90% chance if you get my meaning
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