We need some basic information to calculate average atomic mass: the exact atomic weight for each naturally-occurring stable isotope and its percent abundance. The atomic weight of the isotope takes into account the mass of the electrons. In these examples atomic weight and percent abundance is given.

Interactive exercise. Assistance may be required. Click through the following slide show for step by step instructions on how to calculate average atomic mass.

Video segment. Assistance may be required. Review the process by watching the following short video.

Source: Average Atomic Mass, Chemtracker, YouTube