Chemistry
posted by Heather .
Average density of a coppercoated iron BB is 8.00g/mL. If the density for copper is 8.92 g/mL, and the density for iron is 7.43g/mL, what is the percentages of copper and iron in a BB?

Notice that mass is density*volume.
total mass=massiron*densityiron*volume + masscopper*densitycopper*volume
Now, divide by total mass
1= fractioniron*densityiron*volume/mass + fractionCu*densityCu*volume/mass.
now note that volume/mass=1/avgdensity
and that fractionCu=1fractioniron
That should be enough for you to grunt through the algebra. 
I am confused on what the fraction is?? and what is my volume? could you please clear this up?