Question

the sum of the weight of an iron piece and the copper piece is twice that of the Iron Fist if the weight of 1 cubic centimetre of iron is 7.8 gram and that of copper is 8.9 gram find the volume of each piece

Answer 1

Mass of iron=mi=vixdi where v&d are vol and density 
mass of copper=mc=vcxdc 
mi+mc=1280 gms and vc=2xvi 
vixdi+vcxdc=1280 
vixdi+2vixdc=1280, now,di=7.8/cc & dc=8.9 
putting the values we get, 
vix7.8+2xvix8.9=1280 
vix7.8+17.8vi=1280 
25.6vi=1280 , therefore,vi=50cc,thus vol of copper=vc=2vi=100cc