Two parallel plate capacitors $\mathrm{C}_1$ and $\mathrm{C}_2$ each having capacitance of $10 \mu \mathrm{~F}$ are individually charged by a 100 V D.C. source. Capacitor $C_1$ is kept connected to the source and a dielectric slab is inserted between it plates. Capacitor $\mathrm{C}_2$ is disconnected from the source and then a dielectric slab is inserted in it. Afterwards the capacitor $\mathrm{C}_1$ is also disconnected from the source and the two capacitors are finally connected in parallel combination. The common potential of the combination will be $\_\_\_\_$ V.
Assuming Dielectric constant = 10)