Hi Takako "sounds about right" is not quite the same as "sounds right", because 'about' in this context has a meaning of "approximately"

Yes, it is the same meaning. "Sounds about right" can be used when the person is mostly sure of something, but could be wrong. I'm not sure why we add "about", but the meaning is virtually the same. Adding "about" could indicate a little bit of uncertainty over "sounds right".

all the explanations above sound about right. :P

That's about right = その通りかな。