Here work done on gas and heat supplied to the gas are zero. Let T be the final equilibrium temperature of the gas in the vessel. Total internal energy of gases remain same. i.e., u1+u2=u1′+u2′ or, n1CvδT1+n2CvΔT2=(n1+n2)CvT ⇒(0.1)Cv(200)+(0.05)Cv(400)=(0.15)CvT ∴T=