Question

Three rings each of mass m radius r are so placed that they toucb each other the radius of gyration

Answer 1

I suppose you need the radius of gyration from the centre of the second ring  Just add up the moment of inertia by every ring and the distance they need to cover to the centre of second ring^2* mass of the ring MR^2 + 4MR^2 + 4MR^2 It would be  9MR^2 = MX^2  Thus  X=3R