1. Calculate the abundance of each isotope in your sample. Show all work and convert your fraction to a decimal.
Abundance = # of pennies for an isotope/Total # of pennies

2. Calculate the average mass of each isotope. Show all work.
Average mass = Total mass of pennies of each isotope/ Number of pennies of that isotope

3. Calculate the average atomic mass of Pe. Show all work.
Average atomic mass = (abundance isotope 1 x average mass isotope 1) + (abundance isotope 2 x average mass isotope 2) + ...