A graduated cylinder contains 20.0 mL of water. An irregularly shaped object is placed in the cylinder, and the water level rises to the 31.2-mL mark. If the object has a mass of 7.42 g, what is its density?

According to Archimedes principle, when an object is submerged in water, it displaces a volume of water equivalent to the volume of the object. Therefore, the object's volume is:

31.2 - 20 = 11.2 mL

Next, we know that the density of any substance is the ratio of the substance's mass to its volume, so the density is:

Density = mass / volume

Density = 7.42 / 11.2

Density = 0.66 grams per mL