1. The problem statement, all variables and given/known data "An alloy of copper and tin has a volume of 100cm^3. The density of the copper is 8900 kgm^-3 and tin 7300kgm^-3. How much volume of each metal must be used if the alloy is to have the density of 7620kgm^-3? 2. Relevant equations Volume x density = Mass 3. The attempt at a solution I've worked out the total mass, (100x10^-6 x 7620 = 0.762kg). From here I try to re-arrange this equation x + y = 1x10^-4m^3. X = The volume of copper and Y = the volume of tin. I don't know them, so I get x = 1x10^-4m^3 - y 0.762kg/8900kgm^-3 = 1x10^-4m^3 - y 8.89...x10^-5m^3 = 1x10^-4 - y (Doing the calculation of 0.762kg/8.89...m^3) -1.101123...x10^-5m^3 = -y Subtracting 1x10^-4 from both sides 1.1011..x10^-5m^3 = y Times by minus 1 Then (1x10^-4) - y = 8.898876x10^-5m^3 x = 8.898876x10^-5m^3 Copper volume(x) = 8.898876x10^-5m^3 Tin volume(y) = 1.1011..x10^-5m^3 I think that is right, but I'm doubting if it is right or not. Reasoning being I divided the total mass by the density of x (copper). Can I do that to work out the volume of x and sub it into that equation? Because logically in my head that does not work. Unless I'm mis-understanding something.