What is the vapor pressure of a solution with a benzene to octane molar ratio of 2 1?

At 50 °C the vapor pressure of Benzene is 280 mmHg while that of Octane is 400 mmHg.

Mole Fraction of Benzene;

                           2 / 2 + 1 = 0.666

So, Vapor pressure of Benzene is,

                           0.666 ×  280 mmHg  =  186.66 mmHg

Mole Fraction of Octane;

                           1 / 2 + 1 = 0.333

So, Vapor pressure of Benzene is,

                           0.333 ×  400 mmHg  =  133.33 mmHg

Vapor Pressure of Solution;

             Vapor pressure of Benzene + Vapor pressure of Octane

                          186.66 mmHg  +  133.33 mmHg  =  319.99 mmHg