If the moment of inertia of a disk kept in xz plane about x and y axis are, respectively, 30 kgm2 and 40 kgm2, then moment of inertia about z-axis (in kgm2) will be

According to the perpendicular axis theorem,Ix+Iz=IyWhere Ix and Iz are the moment of inertia of planer object about the x and z axis respectively, which lie in the same plane of the body. Iy is moment of inertia of the object about y axis which is perpendicular to the plane of the body.According to the given question:30+Iz=40⇒Iz=10kgm2