A uniform solid sphere of mass m and radius r is surrounded symmetrically by a uniform thin spherical shell of radius 2r and mass m

$\begin{array}{l}\text{The gravitational field at a distance of 2.5r }\left(\text{or}\right)\frac{5}{2}\text{r from the centre is }\\ \left(out side both the spheres\right)\\ \mathrm{E}=\frac{\mathrm{Gm}}{{\left(\frac{5}{2}\mathrm{r}\right)}^2}+\frac{\mathrm{Gm}}{{\left(\frac{5}{2}\mathrm{r}\right)}^2}=\frac{8\mathrm{Gm}}{25{\mathrm{r}}^2}\end{array}$