%Fe = mFe/Mamestec ×100
75 = (56x+112y)/(56x+160y)×100
75(56x+160y) = 5600x+11200y
1400x=800y
x/y = 7/4
4 moli Fe, 7 moli Fe2O3
m Fe = 4×56= 224g
m Fe2O3 = 1120g
Fe : Fe2O3 = 224:1120 = 1:5
Verificare: m amestec = 1344g
m Fe amestec = 1008g
% Fe = 100800/1344 = 75