Simple mathquestion PLEASE HELP

programming flash
1

I have a slider that I want rounded to the closest 100 and it should start from 0 to 5000.

The code I’m using is the following:

onMouseMove = function(){
updateAfterEvent();
}

var num:Number = 52.3;
num /= 100;
num = Math.round(num);
num *= 100;
trace(num);

this.ratio=0 ;
dragger.onPress=function(){
this.startDrag(true,0,0,line._width,0);
this.onEnterFrame=function(){
ratio=Math.roundCOLOR=red * 10000 / num[/COLOR];
}
}

the slider is 385px x-width which makes it even harder to get it to 5000
385 * 12,98701 = 5000

HALP!