Which three types of information are needed to calculate an average atomic mass?

Question

The percentage abundance of each isotope.

The neutron mass.

The proton mass.

The masses of the isotopes on the carbon–12 scale.

The number of isotopes that exist for the element.

The atomic number for the element.

Answer 1

You need the percentage abundance and the masses of each isotope.

You then take a "weighted average" by multiplying % (in decimal form) x mass and sum them to get the average.