this problem should be simple, but i must be doing it wrong. At 250 degrees Celsius, a certain liquid X has a vapor pressure of 900 mm Hg and a second liquid Y has a pressure of 600 mm Hg. What is the minimum mole fraction of X necessary for the mixture to boil at this temperature (assume atmosphere pressure is 1 atm). MY WORK: Since I know that the total pressure at this temperature is 1500 mm Hg, and only 760 mm Hg is needed, then only about 51% of the pressures are needed. But when I do (51%)(900) and (49%)(600), it doesn't add up to 760 mm Hg. When I do guess and check, i get about 53.3% of compound X. How do you do this problem! Thank you.