Two parallel plate capacitors C1 and C2 each having capacitance of 10µF are individually charged by a 100V 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 )