I just need a little help with this question..how should I finish a problem like this? In a sample of 18-karat gold, 75 percent of the total mass is pure gold, density_gold = 19.3 g/cm^3, while the rest is typically 16 percent silver density_silver = 10.5 g/cm^3 and 9 percent copper density_copper = 8.9 g/cm^3. If the density of pure gold is , while the densitites of silver and copper are respectively and , what is the overall density (density_18k) of this alloy of 18-karat gold? Express your answer in grams per cubic centimeter to three significant figures. I first thought of the formula D = M/V and went from there. I got the mass of pure gold in 1 gram of alloy, which was just .75. Then I got the volume of it, which was 3.89 *10^-2. But when I did mass/volume, I just got 19.3. They are asking for the overall density of the 18 karat gold sample, so I just added all three densities and my answer was wrong. So, I'm stuck b/c I think I was just going in circles for this problem. And can any of you tell me why it didn't work when I added them all up b/c it didn't make sense.