This is for my chemical engineering class...for some reason, I am struggling with this problem. I'm not quite sure how to connect the dots..I feel like I know how to do this, though. 1. The problem statement, all variables and given/known data The mass fraction of benzene in a benzene-toluene mixture is 0.450. What is the mole fraction of toluene in the mixture? Molecular weights of benzene and toluene are 78.11 and 92.12 respectively. 2. Relevant equations listed 3. The attempt at a solution Mass fraction of toluene is .550 Now, that is dimensionless, and I don't know how to get going from here. I know it's simple, but I've forgotten my general chemistry... I was thinking I just multiply that mass fraction by the molecular weight of toluene, but then that's still in g/mol...then I thought about adding them, which would make more sense (since I have the mass fraction). I dunno though, because I don't have the exact chemical formula. Any tips or steps would be greatly appreciated. Thank you.