I'm taking an introductory geology class and am having big trouble with the math questions, as it's been many many years since I last took math classes. I am to use Archimedes Principle to calculate the thickness of continental crust beneath a certain coastal geographical point (at sea level and not accounting for post glacial rebound effects). Data given: Water depth to the abyssal plain: 5000m Thickness of abyssal oceanic crust: 10000m Density of continental crust: 2800 kg/m3 Density of oceanic crust: 3000 kg/m3 Density of mantle: 3300 kg/m3 Density of water: 1000 kg/m3 Our course material does not include any formula for Archimedes Principle, just a brief description of how it works. So, I've googled to find a formula, but really am having a hard time understanding what it is I'm looking at. I have the basic formula, but I'm not seeing how I should use it to get what I need: Apparent immersed weight=weight-weight of displaced fluid. I understand that the fluid here is the mantle, with density given for it, and of course the cont. crust density appears relevant, but that's about as far as I can get with this! And I don't understand why there is data for oceanic crust, water depth and density of water.... I'm assuming there are some other formulas involved in this calculation. I know thickness can be calculated from Volume=height*length*width. But nothing in the data seems to hint at length or width....?? aaah, this is so confusing, I don't know where to begin even. Any hints or tips will be greatly appreciated.