the method is... let number ofFe2+ be x and number of Fe3+ be y so x+ y=93 balancing charge with that of oxygen we get 2x + 3y = 200 solving these 2 eqns we get y= 14 so %age = 14/93 *100= 15 % approx
rohit it's 15.05 what method did you use to get 76.5%? If you want the solutions have a look at the other post of this question. Some ppl have answered there.