So I'm trying to determine the magnetic permeability of an area that contains multiple substances. let's say i have some volume $V$ that is filled with two substances, one is iron filings and the rest is some non-magnetic viscous fluid such that the iron is suspended in it. Let's say the iron filing are taking up 10% of the volume. Let's say the magnetic permeability of the iron filings is $\mu_1$. Can i treat this volume as if it has a magnetic permeability of $\mu = 0.1*\mu_1$ since the iron filings are the only magnetic material.
If so, could i do the same thing with a mix of two magnetic materials that have permeability $\mu_1$ and $\mu_2$? If material 1 is taking up 25% of the volume and material 2 is taking up 75%, could i consider this volume to have a permeability of $\mu = 0.25*\mu_1 + 0.75*\mu_2$
Thanks for any clarification!