Chemistry (7th Edition)

The atomic weight of copper is equal to $63.55$; This is the same value that appears on the periodic table.
Remember, 100% represents 1.00, which means that 69.15% represents 0.6915, and 30.85%, 0.3085. Atomic weight = (62.93)(0.6915) + (64.93)(0.3085) = $63.55$