Mass functions from the observed sample and our population synthesis simulation. The input initial mass function (IMF) used in the population synthesis is shown in green. The blue solid line represents the present day mass function (PDMF) of all stars in the simulation. The blue dashed line gives the PDMF of the stars which successfully pass our selected effect filters, in comparison the PDMF of all B-type stars of the observed LMC sample, including those for which no nitrogen measurement is available (red line) . The synthesized mass functions have been scaled by a factor of 1/500 for ease of comparison with the observed distribution.