There are 2 spheres. 1 is massive and the density linearly decreases, with each shell of the sphere of equal thickness having the same mass.
Density at any Radius*Volume of Layer with constant width=Constant Mass
Additionally, there is a second sphere, this time hollow, which has the same mass as a layer of the same width as before.
Assuming the second sphere can move freely through the first, and that it is centered around the others center, how would I calculate the gravitational forces acting upon it at different radii?