Two binary solutions of different compositions or even two pure components can be mixed with various mixing ratios by masses, moles, or volumes.
The mass fraction of the resulting solution from mixing solutions with masses m and m and mass fractions w and w is given by:
where m can be simplified from numerator and denominator 
and
is the mass mixing ratio of the two solutions.
By substituting the densities ρ(w) and considering equal volumes of different concentrations one gets:
Considering a volume mixing ratio r
The formula can be extended to more than two solutions with mass mixing ratios 
to be mixed giving: