1. The problem statement, all variables and given/known data A spherical aluminum ball of mass 1.26 kg contains an empty spherical cavity that is concentric with the ball. The ball just barely floats in water. Calculate a.) the outer radius of the ball. b.) the radius of the cavity. 2. Relevant equations I think I have it this time; d(fluid)gV(object) = m(aluminum)g d(fluid)(4/3(pi)(r^3)) = m(aluminum) I solve this for r, and that is the answer for part a. Next, V(object) = 4/3(pi)(r^3) i sub in the radius i found in part a to find V(object) Next, V(aluminum) = m(aluminum)/ d(aluminum) and solve for v aluminum I then subtract, V(cavity) = V(object) - V(aluminum) Finally, 4/3(pi)(r^3) = V(cavity), and solve for r, this is the answer for b. 3. The attempt at a solution I think this is the right setup for this problem. My only problem is where do I find the values for aluminum and the fluid?