1. The problem statement, all variables and given/known data Aluminium-Lithium alloys have been developed by the aircraft industry to reduce the weight and improve the performance of its aircraft. A commercial aircraft skin material having a density of 2.47 g/cm3 is desired. Compute the concentration of Li (in wt%) that is required. 2. Relevant equations 3. The attempt at a solution I've calculated the atoms/cm3 for both aluminium and Lithium, but i'm not sure how to relate them seeing as the question doesn't give an amount/quantity of either element. I assume there is an equation or something I should use but I can't think of it.