How many places does a fact have to appear to be considered common knowledge for bibliographical purposes?

Question

Exactly what the question says.

Answer 1

That is not really the point. A fact can be in many many places and you still need to cite it. If it is so commonly known that a typical person would not have to look it up (Elvis is dead) then you do not need a citation.

The problem is that this is a judgement call. When in doubt, ask your teacher/professor. Or otherwise, when in doubt, provide a citation.

Answer 2

3 of your sources