Soil Physics: Mixing different soils

[sfd101]

This is a lab question I have for Environmental Soil Physics. Been thinking about it for awhile and I have nothing.

What would be the average particle density of a mixture of 3% soil organic matter and 97% soil minerals by weight. Soil orgainc matter and soil minerals have densities of 1.37g/cubic centimeter and 2.73g/cubic centimeter, respectively.

According to the prof., the answer should be ~2.65g/cubic centimeter, which is the average value for mineral soils.

I have tried using a ratio of 3% soil organic matter and 97% soil minerals and multiplying it by the total density. Just like if it is 50% of each. However, it is not close to 2.65g/cubic centimeter. I just need a point in the right direction.

Thanks.

 

[GCT]

Take 3% of 1.37g/cubic centimeter and 97% of 2.73g/cubic centimeter and then add the two values.