What symbol is used for the arithmetic mean when it is a sample statistic? Also;

What symbol is used when the arithmetic mean is a population parameter?

I am a bit confused on those two questions. I have the Understanding basic statistics book and I've gone over the chapter reviews but I am just not getting it?

I know that the "Means is the average usually used to compute a test average" at least I think that's correct, but what are the symbols? I thought the first question was a "small n" and the second question was a "large N" but I am not so sure now?

Or maybe it's that weird looking ex and I put the small n under it? the same with the other one?

Can anyone help me on this?

Thank you

Cece