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A common way to compute density is, of course, to take the ratio of an object's mass to its volume. But other types of densities exist, such as the resistance of somebody's brain to the imparting of common sense.

Neil deGrasse Tyson (2007). “Death by Black Hole: And Other Cosmic Quandaries”, p.135, W. W. Norton & Company
A common way to compute density is, of course, to take the ratio of an object's mass to its volume. But other types of densities exist, such as the resistance of somebody's brain to the imparting of common sense.