If we mix two liquid with the same volume;

$latex d_{mixture} = \frac {d_{1} + d_{2}} {2} $

If we mix two different liquid with the same mass:

$latex d_{mixture} = \frac {2 d_{1} d_{2}} {d_{1} + d_{2}} $

Where $latex d_1 and d_2 $ are different liquids that are to be mixed.

$latex d_{mixture} $ is the mixture’s density.