A geode is a hollow rock with a solid shell and an air-filled interior. Suppose a particular geode weighs twice as much in air as it does when completely submerged in water. If the density of the solid part of the geode is 3100 km/m^3 , what fraction of the geode's volume is hollow? The density of air is 1.20kg/m^3 and density of water is 1000, and I have been trying to use the equation Fb (force of buoyancy) = W (weight of the object) (I use the symbol ρ for density) I have: Fb=w ρ_water(volume)g=ρ_geode(volume)g2 and Vair/Vgeode as my unknown... I'm confused on what densities to use.. and if I'm even on the right track. Any help would be appreciated!