1. The problem statement, all variables and given/known data A hollow sphere has a mass of 15 kg, an inner radius of 12 cm and an outer radius of 18 cm. What is the rotational inertia (moment of inertia) of the sphere about an axis passing through its center? 2. Relevant equations 3. The attempt at a solution I = 2/3 MR^2 for a hollow sphere so i did this: 2/3 (15) (.18^2) = .32 kg m^2 But this is wrong the answer is .24 kg m^2. Any thoughts?