A solid sphere of uniform density and radius R applies a gravitational force of attraction equal to `F_(1)` on a paticle placed at a distance 3R from the centre of the sphere. A spherical cavity of radius `R//2` is now made in the sphere as shoem in the figure. The sphere with cavity now applies a gravitational force `F_(2)` on the same particle. The ratio `F_(2)//F_(1)` is