An iron ore sample contains Fe₂O₃ plus other impurities. A 747-g sample of impure iron ore is heated with excess carbon, producing 456 g of pure iron by the following reaction.

Fe₂O₃(s) + 3 C(s) 2 Fe(s) + 3 CO(g)

What is the mass percent of Fe₂O₃ in the impure iron ore sample? Assume that Fe₂O₃ is the only source of iron and that the reaction is 100% efficient. %