I don't understand this stoich problem ;-;

[MathematicalMistake]

A 26.6 g sample of impure potassium nitrate (KNO₃) was heated to complete decomposition according to the equation
2 KNO₃(s) → 2 KNO₂(s) + O₂(g) .
After the reaction was complete, the solid residue (consisting of KNO₂ and the original impurities) had a mass of 23.1 g. Assuming that only the potassium nitrate had decomposed, what was the percent KNO₃ in the original sample?
Answer in units of %.

I did this: (2 *(26.6 - 23.1)*101.103*100% ) / (32.00)(26.6)
which got 84%, but it says I'm wrong. Please help

[ChenBeier]

I got the same amount.
3,5 g O₂/ 32 g/ mol is 0,11 mol
This correspond to the double of KNO₃ means 0,22 mol
Multiplied with molar mass 101 g/mol = 22,1 g
Percentage is 22,1/ 26,5 = 0,83 => 83%

[MathematicalMistake]

Ok, thank you. I actually found a slight mistake in my method!