Compare the density of copper with the value for the slope of the line for the pre-1982 pennies

Pennies minted prior to 1982 should have a density almost the same as pure copper (8.96 g/cm3) while pennies minted after 1982 should have a density almost the same as pure zinc (7.14 g/cm3). Pennies are 97.6 percent zinc and 2.4 percent copper, giving them a density of 7.15 g/cc - the lowest of any US penny.

Explanation:

it is the most commonly accepted one

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