1. The problem statement, all variables and given/known data Water corresponds to approximately 20 vol.% of the bone in mammals. On a dry weight basis, approximately 70 wt.% of the bone is composed of carbonated apatite. The density of apatite is ~3.0 g/cm3. Density of dry collagens is ~ 1.2 g/cm3. Calculate the volume percentages of apatite and collagen in dry bone. Calculate the volume percentages of water, apatite and collagen in bone in vivo. 2. Relevant equations Vf = (Wf / ρf) / (Wf / ρf + Wm / ρm) where Vf = Volume fraction, Wf = Weight fraction of filler, Wm = Weight fraction of maxtrix, ρm and ρf = Density of matrix and fiber respectively 3. The attempt at a solution Regarding the dry bone, it contains 70 wt.% of carbonated apatite and 30 wt% of collagens. Volume percentages of carbonated apatite: vf = [(70/3) / (70/3 + 30/1.2)] *100 vf = 48.3 % Volume percentages of collagens: vf = [(30/1.2) / (70/3 + 30/1.2)]*100 vf = 51.7 % Regarding the bone in vivo, it contains 20 vol.% of water and 80 vol% of carbonated apatite and collagens. Volume percentages of carbonated apatite: vf = 48.3*0.8 = 38.6 % Volume percentages of collagens: vf = 51.7*0.8 = 41.4 % I know this is a standard textbook question but I am really wondering whether I am wrong or not. Can anybody please give me some opinion? Cause I think it is too simple for this question...Thank you so much.