# 2. The element copper has naturally occurring isotopes with mass numbers of 63 and 65. The relative abundance and atomic masses are 69.2% for a mass of 62.93 amu and 30.8% for a mass of 64.93 amu. How do you calculate the average atomic mass of copper?

And thus the $\text{weighted average}$ is:
(62.93xx69.2%+64.93xx30.8%)*"amu" $=$ $63.55$ $\text{amu}$