Two parallel plate capacitors C₁ and C₂ each having capacitance of 10$\mathrm{\mu }$F are individually charged by a 100 V D.C. source. Capacitor C₁ is kept connected to the source and a dielectric slab is inserted between it plates. Capacitor C₂ is disconnected from the source and then a dielectric slab is inserted in it. Afterwards the capacitor C₁ 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)