According to Raoult's law P0P0−PS=N1+N2N1; ∴1−P0PS=N1+N2N1
or P0PS=1−N1+N2N1=N1+N2N2
or PS=P0×N1+N2N2
Also we can derived from P0P0−PS=N1+N2N1 ∴P0−PSP0=N1N1+N2=N1N2+1
or P0−PSPS=N1N2
or PSP0−PS=N2N1