A chemist wants to determine the molar mass of a naturally occurring substance isolated from spearmint. She adds 4.831 g of this substance to 25.00 g of acetone (C3H6O; molar mass 58.08 g/mol). The vapor pressure of the solution is determined to be 0.2454 atm at 25°C. If the vapor pressure of pure acetone at this temperature is 0.2630 atm, what is the mole fraction of the solvent in this solution? Give your answer to four significant digits.