Red gold is a gold‑copper alloy used to make jewelry. A piece of jewelry made of red gold weighs 7.80 g and has a volume of 0.475 cm3. Gold has a density of 19.3 g/cm3 and copper has a density of 8.96 g/cm3. Calculate the percentage by mass of each metal in the jewelry. Assume the total volume of the jewelry is the sum of the volumes of the two metals it contains.