1. The problem statement, all variables and given/known data What diameter must a helium filled balloon have to float with neutral buoyancy? The mass of the empty balloon is 2 g. 2. Relevant equations FB = (density)(gravity)(Volume) Volume of balloon = 4/3(4.13)r^2 Density = mass/Volume 3. The attempt at a solution I know that the balloon will float when its weight is equal to the weight of the air displaced. Weight of balloon = Weight of air displaced Weight of empty balloon = 0.002kg x 9.81 = 0.01962N Thus weight of air displaced = 0.01962N But this is a far as I am getting as I am very confused with where the density plays a roles since no densities is given in this problem.