The mass, volume and density of hollow iron balls and solid iron balls vary greatly.

We can base it on: volume = mass/density.

When two steel balls have the same mass, there is air in the hollow steel ball, so the average density is less than that of steel, while the density of solid steel ball is equal to that of steel, so it can be concluded that the density of hollow steel ball is less than that of solid steel ball by comparison.

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