Get Parent Width, Calculate difference as Percentage

gistfile1.js

$('#nav-1 li .dropdown').each(function(){
			var parent_width = (((($(this).width() - $(this).parent().width()) / '2') / $(this).parent().width()) * '100') + '';
			var percent_round = Number(parent_width).toFixed(2);
			$(this).css('margin-left' , '-' + (percent_round) + '%');
		});