[nitpick]Actually, faq, the zero fuel weight on landing will be the difference between (a) the total weight of pax + food at takeoff; and (b) the matter that was converted to energy by the pax from the effort of getting up to use the toilet, reading and flirting with the hosties. The old standby E=MCwhatever thingy that Einstein fella came up with will help you with the sums on that.[/nitpick]