1. The problem statement, all variables and given/known data What is the average density of rock in the mantle? The earth's average density is 5500 kg/m^3; the radius of the core is 3490 km; ratio of core density to mantle density is 2.34 2. Relevant equations Pc = density core Pm = density mantle Pe = density earth Mm = mass mantle Mc = mass core Rm = radius mantle Pc/Pm = 2.34 so Pc/2.34=Pm Pm = Mm/(4/3)*pi*Rm^3 Pc = Mc/(4/3)*pi*(3.49E6)^3 Rm = Re - Rc Assume only the core and mantle compose the earth. Mc/Vc + Mm/Vm = Me/Ve = Pe = 5500 (?) 3. The attempt at a solution Pc/2.34 = Pm = (Mc/(4/3)*pi*(3.49E6)^3)/2.34 I'm not sure what equation would give me Mc, the mass of the core. My other equation had the radius of the earth as a variable. I think I'm just missing one equation, but I can't seem to find another relationship.