Methylbenzene and 1,2-dimethylbenzene mix to form an ideal solution. At 90oC, the vapor pressure of pure methylbenzene is 400 Torr and that of pure 1,2-dimethylbenzene is 150 Torr.
What is the composition of a vapor mixure (XA, XB) that boils at 90oC when the total pressure is 270 Torr (A=methylbenzene, B=1,2-dimethylbenzene)?