What will be the force constant of the spring system shown in the figure?

 

For parallel combination of first two identical springs of spring constant ${\mathrm{k}}_1$, effective spring constant

${\mathrm{K}}_{\mathrm{p}} = 2{\mathrm{k}}_1$

Now, springs of spring constants ${\mathrm{k}}_{\mathrm{p}} \mathrm{and} {\mathrm{k}}_2$ are joined in series, so the force constant or the spring constant of the system is

$\frac{1}{{\mathrm{K}}_{\mathrm{S}}} = \frac{1}{{\mathrm{K}}_{\mathrm{P}}}+\frac{1}{{\mathrm{K}}_2} = {(\frac{1}{2{\mathrm{k}}_1}+\frac{1}{{\mathrm{k}}_2})}^{-1}$