How to determine total vapour pressure of solution in liquid phase as well as gas phase ?

According to Raoult's Law: The partial pressure of any volatile component of a solution at any temperature is equal to the vapour pressure of the pure component multiplied by the mole fraction of that component in the solution.

      Where X_A­ and X_B is the mole fraction of the component A and B in liquid phase respectively

According to Dalton's Law:

The vapour behaves like an ideal gas, then according to Dalton's law of partial pressures, the total pressure P_Tis given by:

 Partial pressure of the gas = Total pressure x Mole fraction

                                        P_A = P_T Y_A and P_B =P_T Y_B

Where Y_A­ and Y_B is the mole fraction of the component A and B in gas phase respectively

Combination of Raoult's and Dalton's Law:

(3) Thus, in case of ideal solution the vapour phase is phase is richer with more volatile component i.e., the one having relatively greater vapour pressure