${P_T}\, = {\chi _A}P_A^o + {\chi _B}P_B^o\, = 0.4\, \times \,7\, \times \,{10^3}\, + \,0.6\, \times \,12\, \times \,{10^3}\, = \,{10^4}$
$0.4\, \times \,7\, \times \,{10^3}\, = \,{Y_A}\, \times \,{10^4}$
${Y_A}\, = \,0.28$
${Y_B}\, = \,1 - 0.28\, = 0.72$
[ઉપયોગ : ${R}=0.083\, {~L}\, bar \,{mol}^{-1} \,{~K}^{-1}$ ]