Multiples of a number

I'm trying to figure out a code about having reward in every multiples of a number. I can't seem to find a tutorial of this.
Example in score like every 20 points you get an item, like it reaches 40,60,80,.. and so forth.. Doing manually till 999999 is pain the A##.
So how do we do things in just 1 code for a multiples of a number?

Attribute : Score = (every 20 score points?)
Spawn reward.