Scroll Chance Bonus.

oh, you guys meant that way for multiplicative. I thought he meant it like most other "multiplicative" terms in gaming. Like if you have 2 20% dodge chance skills, your dodge chance isn't 20%+20% nor 20%*1.2= 24% but 36% instead (1 - .8*.8).

That's not "multiplicative"; that's a sequence of events.

The 'dodge' scenario describes the odds of not getting hit by an attack after two attempts to dodge.
If the first dodge fails, there's a 20% chance of dodging on the second attempt, but since there's only a 80% chance of this attempt happening this outcome only has a 16% chance of occurring (.8 * .2 = .16).
Since there's a 20% chance of dodging on the first attempt and an 16% chance of dodging on the second attempt, the chance of dodging at all is 36%.

Trying to use this formula when it comes to scrolling in Maplestory means that you're treating the the Diligence bonus as another roll.
Of course, this makes no sense since nothing in any version's text would lend to that conclusion.

And that is why it's important to understand the formulas you use: so you can use them appropriately.