Answer
One measurement gives us the mass, and the other gives the volume of the object. Knowing M and V, calculate $\rho$ with 15-1.
Work Step by Step
The density, $\rho$, of a material is its mass M per volume V:
$\rho=\mathrm{M}/\mathrm{V} \qquad $ 15-1
To calculate $\rho$, we need to find its mass and volume.
Weighing it in air, we find its mass from $\mathrm{F}_{\mathrm{g}}=\mathrm{M}\mathrm{g}.$
Weighing it together with the water, we find its volume, as we know that $\rho_{\mathrm{w}}=1\mathrm{k}\mathrm{g}/\mathrm{m}^{3}$
