Two disc one of the density 7.2 gm/cc and other of density 8.9 gm/cc are of the same mass and thickness their moment of inertia are in the ratio of ……
$ { I_1 \over I_2 } = { { 1\over 2 } M_1 R_1^2 \over { 1 \over 2 } M_2 R_2^2 } = { R_1^2 \over R_2^2 } $