1. The problem statement, all variables and given/known data A planet or radius R has a core of radius R/3 and density 2d, a middle layer from radius R/3 to 2R/3 and density d/2, and an outer shell from radius 2R/3 to R and a density of d. What is the average density as a whole? 2. Relevant equations d=m/v 3. The attempt at a solution Not sure where else to stick this question so I put in the basic math section here (if it's the wrong section please do move it). I figured that to solve this question I would need to simple add all 3 density values given together and divide by 3. This seems too easy, however, and i'm not sure if I can treat the mass as a constant. Would this be the right method or am I missing something here? If anyone could be of assistance it would be greatly appreciated, thanks in advance.