Each type of penny contributes a different amount to the overall mass We can calculate the amount each type contributes by using the abundance in decimal form and the average mass of the penny type Post 1982 mass decimal abundance average mass Sample Pre 1982 Post 1982 Number of Pennies 8 12 Abundance 9 40 60 Average Mass g 3 1 2 5 What mass do the post 1982 pennies contribute