Kinetic Theory of Gases

Question: Three containers of the same volume contain three different gases. The masses of the molecules are ${{m}_{1}},\,{{m}_{2}}$ and ${{m}_{3}}$ and the number of molecules in their respective containers are ${{N}_{1}},\,{{N}_{2}}$ and ${{N}_{3}}$. The gas pressure in the containers are ${{P}_{1}},\,{{P}_{2}}$ and ${{P}_{3}}$ respectively. All the gases are now mixed and put in one of the containers. The pressure P of mixture will be