Answer
$250\space kg/m^{3}$
Work Step by Step
Here we use the principle of Archimedes' to find the average density of the duck.
$W_{water}=W_{duck}$
$\rho_{w}V_{w}g=\rho_{d}V_{d}g$
$\rho_{w}\frac{V_{d}}{4}g=\rho_{d}V_{d}g$
$\rho_{d}=\frac{\rho_{w}}{4}$ ; Let's plug known values into this equation.
$\rho_{d}=\frac{1000\space kg/m^{3}}{4}=250\space kg/m^{3}$
Average density of the duck $=250\space kg/m^{3}$
