A graduated cylinder is partially filled with water; a rubber duck floats at the surface. Oil is poured into the graduated cylinder at a slow, constant rate, and the volume marks corresponding to the surface of the water and the surface of the oil are recorded as a function of time.
Water has a density of 1.00 \mathrm{~g} / \mathrm{mL}; the density of air is negligible, as are surface effects. Find the density of the oil.