1. The problem statement, all variables and given/known data I'm running a simulation and was given 2 mass flow rates (let's say m1_dot and m2_dot) for 2 chemical species at the inlet. 2. Relevant equations mass flow rate = density*velocity * area 3. The attempt at a solution I need to compute the bulk velocity for the fluid (consisting of the 2 species), so it needs to be some mass-weighted average that I'm computing, but how can I do this when I don't know the mass fractions?