Titration calculations - confused

A sample (1.1534g) of a tin containing substance was converted into an aqueous Sn2+ solution with a total volume of 250 cm^3. Three 25 cm^3 aliquots of this Sn2+ solution were titrated with a KMnO4 solution of concentration 1.78 x 10^-2M. The titres were recorded as 16.53 + 16.49 + 16.56 cm^3.

Calculate the total number of moles of Sn2+ and the concentration of Sn2+ in the original solution.


So i have the equation:
5Sn2+ + 2MnO4- + 16H+ --> 5Sn4+ + 2Mn2+ + 8H2O


Number of moles:

Take the average of the 3 titre volumes: 0.01653 dm^3
1.78x10^-2 * 0.01653 = 2.94 x 10^-4
Divide by 2 and then multiply by 5: 7.35 x 10^-4 moles

Concentration:

(7.35 x 10^-4) / 0.01653 = 0.044 mol dm^-3
Is this at all right, or have I done this completely wrong?

Also, how would I calculate the total mass of Sn and percentage by mass of Sn in the original sample?