Number of moles of first gas =NAn1Number of moles of second gas =NAn2Number of moles of third gas =NAn3If there is no loss of energy thenP1V1+P2V2+P3V3=PVNAn1RT1+NAn2RT2+NAn3RT3=NAn1+n2+n3RTmix⇒Tmix=n1+n2+n3n1T1+n2T2+n3T3