Total chare of the system $=\mathrm{CV}+\mathrm{nCV}$
$=(n+1) C V$
After the insertion of dielectric of constant $\mathrm{K}$ New potential (common) $\mathrm{V}_{\mathrm{c}}=\frac{\text { Total charge }}{\text { Total capacitance }}$
$=\frac{(n+1) C V}{K C+n C}=\frac{(n+1) V}{K+n}$

