A back of the envelope calculation

I was watching my budgies the other day, and had a thought which led to a brief online investigation, followed by the following back-of-envelope calculation: According to a Boeing presentation on airline fuel efficiency that I found on the Internet, a 1% reduction in landing weight gives about a 1% reduction in trip fuel. A Boeing 747’s operational empty weight (with equipment, flight crew etc) is 390,700lbs. Subtracting that from its Maximum Zero Fuel Weight (max weight allowed before fuel is loaded) gives a maximum value for passengers and cargo of 144,300lbs.