Lol dude your math sucks :P
Every time you enchant the chance is the same (40%). Enchanting its a single event and can not be assosiated with other enchants. Try reading some Probabilty Theory, there is all there you need.
But,
The laws of maths are kinda strange. Well lets say you flip a coin, tis 50-50 right. If you do this like 20 times you may get a result of H(Head)-N(Number) of H-H-H-H-D-H-H-D-D-H-H-H-H-H-H-D-H-H etc.
As you see there is no connection between events. But the LAWS of 50-50 MUST be confirmed, so if you do more tryis you ll see in the end that the results are almost the same. So the 50-50 must be confirmed as much tryes your making.
THe case in L2 (and in computer world) is weather the (60-40) is based on true Random fact. I mean can you actually write a code for it?
Most of the cases the code is writen condesing some paterns. As many of Former Soviet Rebublic claim, try to find out the patern and then you are Home Free. I beleive them.
Over and Out