1. The problem statement, all variables and given/known data http://www.xtremepapers.com/CIE/International A And AS Level/9701 - Chemistry/9701_s11_qp_12.pdf question 10 2. Relevant equations 3. The attempt at a solution The way I am doing it, is to get two equations in terms of x and y and then equate them. For the first equation I used the fact that all of the element's individual atomic masses will add up to 571.5. So i got 27x + 28.1y = 172 My problem now is how to get the second equation? I think it has something to do with the empirical formula, but I can't figure it out. Help!