Perfect!
@harpazo
You've done well with these. My only suggestion is for clarity: actaully say how you are representing the numbers. For example, "ab" (or even better [math]10a + b[/math] ) so the sum of the digits is a + b and switching the digits does (whatever). When I was reading your solutions I had to sit and figure out which was the 10s and 1s digits.
-Dan