For those instances where it could be common knowledge--or not--depending on the situation, ask yourself the following questions to help decide if you need a citation:
Who is your audience? What does your reader already know?
In the first case, you might not need a citation, but in the second you should probably include one.
Will your audience/reader wonder where you found the information--and/or question whether it is correct?
The second example is a statistic, and that is one of the categories of information that always needs a citation.
Please contact the Library, the Learning Center, and/or your professor if you need help determining what is and is not common knowledge.