Two thermally insulated vessels 1 and 2 are filled with air at temperature $\left({\mathrm{T}}_{1,}{\mathrm{T}}_2\right)$ ,volume $\left({\mathrm{V}}_{1,}{\mathrm{V}}_2\right)$ and pressure $\left({\mathrm{P}}_{1,}{\mathrm{P}}_2\right)$ respectively. If the valve joining the two vessel is opened , the temperature  inside the vessel at equilibrium will be