Relative atomic mass is an atom's average mass in relation to the number of isotopes and each of their natural abundances.
Using isotopic composition to calculate relative atomic mass: ((Ar of element's isotope*abundance) + (Ar of element's 2nd isotope*abundance) / 100)
The data for percentage abundance may be given in the question, or you will have to determine the ratio/percentage of abundance from given mass spectra by looking at the peaks of each isotope on the mass spectrum.
Note: manipulate this formula at times where abundances may not be given, or when Ar of an isotope is not given to reach an answer.
Using isotopic composition to calculate relative atomic mass: ((Ar of element's isotope*abundance) + (Ar of element's 2nd isotope*abundance) / 100)
The data for percentage abundance may be given in the question, or you will have to determine the ratio/percentage of abundance from given mass spectra by looking at the peaks of each isotope on the mass spectrum.
Note: manipulate this formula at times where abundances may not be given, or when Ar of an isotope is not given to reach an answer.