Two blocks of masses m and 2 m are placed on a smooth horizontal...

Two blocks of masses $m$ and $2 m$ are placed on a smooth horizontal surface as shown. In the first case only a force $f_1$ is applied from left. Later on only a force $f_2$ is applied from right. If the force acting at the interface of the two blocks in the two cases is the same, then $f_1: f_2$ is