# What is the density of a substance that has a mass of 5 g and a volume of 40 cm^3?

It would be $\frac{5 g}{40 c {m}^{3}} = 0.125 g / c {m}^{3}$
In SI units you want to use $k g / {m}^{3}$:
$\frac{0.125 g}{c {m}^{3}} = \frac{0.125 g \times 1000}{c {m}^{3} \times 1000} = 0.125 k g / {\mathrm{dm}}^{3}$
$\frac{0.125 k g}{{\mathrm{dm}}^{3}} = \frac{0.125 k g \times 1000}{{\mathrm{dm}}^{3} \times 1000} = 125 k g / {m}^{3} = 125 k g \cdot {m}^{- 3}$