Using
the table on p68 of CAP697, enter at 50,000kg, note
the max cruise limit of 2994NAM. TAS is 434kts, so in an hour you would travel
434NAM - deduct this from 2994 to give you 2560NAM.
Locate
this figure in the table (or the nearest to it, if necessary) and you will
notice that the weight associated with the distance is now 47,700kg.
Deduct
47700 from 50000kg and you get fuel used to be 2300kg.