Two parallel plate capacitors `C_(1)` and `C_(2)` each having capacitance of `10 mu F` are individually charged by a `100V` D.C.source.Capacitor `C_(1)` is kept connected to the source and a dielectric slab is inserted between it plates.Capacitor `C_(2)` is disconnected from the source and then a dielectric slab is inserted in it. Afterwards the capacitor `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 _______
(Ansuming Dielectric constant `=10` )