1. The problem statement, all variables and given/known data The average density of the body of a fish is 1147.0 kg/m3. To keep from sinking, fish have an air bladder filled with air. If the density of air is 1.28 kg/m3, what percentage of a fish's body must be filled with air to be neutrally buoyant? (Note: Enter your percentage without a unit attached.) 2. Relevant equations /rho avg = Total mass of object / Total volume of object /rho avg = 1000 kg/m^3 3. The attempt at a solution /rho avg = Mo / Vo (Total mass/ divided by total volume) Mo = Ma + Mf (Ma= mass of air and Mf= mass of fish) Ma= 1.28Va (density of air x volume of air) Mf = 1147Vf (density of fish x volume of fish) Now subsituting all the equations together I get... /rho avg = 1000 = (1.28Va + 1147 (Vo-Va)) / Vo and isolating for Va/ Vo = .128 x100% = 12.8 % I also did this to get get Ma / Mo = 0.016% ... but neither answer is right :S. Can anyone tell me what I did wrong, or whether their answer is wrong? Its much appreciated thanks!