A solution contains both iron(II) and iron(III) ions. A 50.00 mL sample of the solution is titrated with 34.80 mL of 0.02800 M KMnO4, which oxidizes all the Fe2+ to Fe3+. The permanganate ion is reduced to manganese(II) ion. Another 50.00 mL sample of the solution is treated with zinc, which reduces all the Fe3+ to Fe2+. The resulting solution is again titrated with 0.02800 M KMnO4; this time 47.80 mL is required. What are the concentrations of Fe2+ and Fe3+ in the (original) solution?