In your case the value becomes formatted string that is not understood as a number. So multiplication does not work.
In Angular it is discouraged to use jQuery to modify DOM, all modifications should be done from Directives. So the best solution is to find the formater directive or create your own. Just search for something like "angularjs mask input".
Or maybe you can create controller and one of its methods will parse your string back into Number. If you still want to stick with jQuery without directive.