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