1. The problem statement, all variables and given/known data " A spherical balloon has a radius of 7.35 m and is filled with helium. How large a cargo can it lift, assuming that the skin and structure of the balloon have a mass of 930 kg? Neglect the buoyant force on the cargo volume itself." 2. Relevant equations So F(b) = (mass of helium + mass of cargo) X 9.8 F(b) = Density of air X volume X 9.8 9.8 cancels out on both sides. Density of air is 1.29 kg/m^3 so 1.29V = (mass of helium + mass of cargo) mass of helium = density of helium (.179) X volume so 1.29V - .179(V) = mass of cargo V for a sphere = 4/3 (pi) (r)^3 = 1663.2 3. The attempt at a solution plug that in and I get 1847.8 for the mass, which is WRONG strangely if I divide that by 2 I get the right answer though... 924, which rounded down would be 920, but I have no idea why id divide it by 2. I do not know what thing is wrong, and please explain detail. I am an international student.