Copper is made of two isotopes. Copper-63 is 69.17% abundant and it has a mass of 62.9296 amu. Copper-65 is 30.83% abundant and it has a mass of 64.9278 amu. What is the weighted average mass of these two isotopes? Show your work.

The weighted atomic mass of these two isotopes is 63.5679 amu. To calculate this first multiply Copper-63's mass of 62.9296 amu by. 6917 which gets you 43.5284. Then multiply Copper-65's mass of 64.9278 by. 3083 which gets you 20.0395. Then add 43.5284 and 20.0395 to get the final answer of 63.5679 amu.