Three block A,B and C of masses 3kg, 2kg and 1 kg are placed on smooth horizontal surface as shown. A horizontal force of 12N is applied on 3kg block. If ${\mathrm{N}}_1$ is the normal force acting between A and B and ${\mathrm{N}}_2$ is the normal force action between B and C, then ${\mathrm{N}}_1/{\mathrm{N}}_2$ is