What are all the values that a mean can possibly take?

Answer 1

A mean can take any value at all. For example, the radius of a normal [human] red blood cell is as small as 3-4 millionths of a metre. By contrast, the mean radius of the earth's orbit is 150 trillion metres. There are, of course, things that are much smaller than red blood cells as well as things whose measures are a lot larger than the earth-sun distance. Means can also take negative values.