Find the sum of average oxidation number of S in H2SO5 and Na2S2O3.

H2SO5  has one peroxide linkage
It means two oxygens has -1 as the oxidation number
And the remaining three oxygens are of -2 oxidation number
Hydrogen is plus one
If we take oxidation number of  sulphur as x
Then X -8+2=0
So it means X here is plus 6
Na2S2O3.
Sulphur here is of two types - one Sulphur atom is bonded  to only one more sulphur and other Sulphur bonded to three oxygen atoms.
Working out oxidation number of these atoms separately ..one is - 2 bonded to sulphur and the other which is bonded to three oxygen is + 6
Average  oxidation number will be plus 6 minus 2 whole divided by 2 + 2