[clockworks204]

At 200k, the vapor pressure of pure xenon is 521 kPa and or pure radon is 58.2 kPa (1kPa=7.50 torr).  How many moles of liquid Rn have to be added to 3.00 moles of liquid Xe to have 0.200 mole fraction of Rn in vapor phase?

A starting point or any help would be appreciated!

[Jorriss]

Raoult's law, there's a starting point.