The in-situ percentage of voids of a sand deposit is $50 \%$. The maximum and minimum densities of sand determined from the laboratory tests are $1.8 \mathrm{~g} / \mathrm{cm}^{3}$ and $1.3 \mathrm{~g} / \mathrm{cm}^{3}$, respectively. Assume the specific gravity of sand as $2.7$.
The relative density index of the in-situ sand is $\_\_\_\_\_\_\_$ (rounded off to $2$ decimal places).