This is with reference to example 23 of H C Verma on Capacitors...A doubt of the -Q/K charge on the negative plate below which is in the dielecric.......

Induced charge on surface of dielectric above lower plate is Q(1-1/K)[By conservation of charge in an isolated system].And due to connection of battery net charge on lower plate is -Q.Again by conservation of charge in an isolated system induced charge on upper surface of lower plate is -Q+Q(1-1/K)=-Q/K.