A solid sphere of mass \( M \) and radius \( R \) is divided into two unequal parts. The smaller part having mass \( \frac{M}{8} \) is converted into a sphere of radius \( r \) and the larger part is converted into a circular disc of thickness \( t \) and radius \( 2R \). If \( I_1 \) is moment of inertia of a sphere having radius \( r \) about an axis through its centre and \( I_2 \) is the moment of inertia of a disc about its diameter, the ratio of their moment of inertia 