Quote Originally Posted by '-silencer-',index.php?page=Thread&postID=76404#post76404

Quote Originally Posted by 'daviddoran',index.php?page=Thread&postID=76111#po st76111
A boss that only drops an specific item 20% of the time will need to be run 10 times to have a 90% total chance of dropping that item. That means that even if you run a boss 10 times, there's a 10% chance of that item not dropping, and that's for an item with a 20% drop rate. It gets much worse for those 5% or 1% drop items!
I'm not sure it works out quite that way... every time you run the instance..you have the same 20% chance (assuming it is in fact 20% chance) to drop the item. It doesn't matter if you run it 100 times..you still only have a 20% chance each time. While odds should say that you should get it by then..there is still a chance you won't....always.