Var x:Number; vs. var x;

1

Hello

what’s the difference between those 2 declares of variables?

*x:Number

x;

*I tried to use xcenter:Number in this code(it’s a infinite image scroller):

var xcenter;
var speed;
var begX;
var endX;

_root.linkholder.onLoad = function() {
	xcenter = _root.mask._x+_root.mask._width/2;
	speed = 2/10;
	begX = _root.mask._x;
}

though it didn’t work, the scroller didn’t move. when I removed* :Number*, it worked though… all the variables are numbers! How does this work?
/regards henxon