[Question] Drop rate how to count ?

oh ya , i forget that is 3 line , ok thx guys , so i think drop rate is only + + + + no *

It's probably a cumulative number before drops are determined.

So:
Base + Mod 1 + Mod 2 + Mod 3 + Mod n = Total Drop Rate

So if you had 3 +20%s
100 + 20 + 20 + 20 = 160% Drop Rate.

The exception is anything that says it's a multiplicative of the value. For example 2x Drop Cards would probably make the above example:
200 + 40 + 40 + 40 = 320% Drop Rate.

This is similar to how EXP is done. You have modifiers that add extra lines, and then you have base modifiers like 2x events and cards that modify the base amount, which then is seen on the modifiers afterwards. Of course, as Stereo said, there's no way for us to know this for certain, however I don't see why it would be any different than the way EXP does it.