For my chemistry class, I need to be able to calculate percent abundances for multiples isotopes, if given the mass of the isotopes and average atomic mass of the element. The percent abundance of 1 isotope may be given. The teacher has said that calculating for a problem with 3 isotopes is all that will be required. However, if possible, I would like to be able to solve a problem with more isotopes, just for future courses. I tried setting up the equation, and I searched my textbook, and have gotten nowhere. The teacher reccomended I search the internet, and I still have gotten nowhere. Can anyone show me how one solves such a problem? Thanks.