A Monte Carlo simulation is performed in order to correlate the average prompt neutron multiplicity as a function of post- and pre-neutron fragment mass (n-(m) and ν-(A), respectively). This is applied for 235,233U(nth,f). The input of the simulation consists of quantities related to pre-neutron fragments, i.e. the mass yield Y(A), the average kinetic energy E-(A), its standard deviation σE(A) and a function ν-s(A) (composed by three jointed segments) which approximates the sawtooth shape of the experimental prompt neutron multiplicity ν-(A). The ratio of neighboring mass yields RA=Y(A+1)/Y(A) is introduced. It is found that n- < ν-s (n- > ν-s) approximately in the same ranges of A where R<1(R>1). The average prompt neutron multiplicity as a function of fragment mass N-μ measured by using the 2E method is also simulated. Its behaviour is similar to the one mentioned above.