$(document).ready( function(){	
	$(".nav li").hover(function(){
		$(this).children(".sub-nav").css('visibility','visible');
	}, function(){
		$(this).children(".sub-nav").css('visibility','hidden');
	});
	$(".nav .sub-nav").hover( function(){ 
		$(this).css('visibility','visible');	
	}, function(){
		$(this).css('visibility','hidden');
	});
});