Help: Calculating the Z-Score CFAI Material Reading 10 examples, everyone, equation, difference

lxwarr30

Good morning, everyone.

I'm having trouble understanding the Z-Score test statistic.

In the reading, a few examples, and the equation for calculating the Z-Score are shown as follows:
Z = (Sample Mean - Population Mean) / Standard Deviation

but there is another equation as follows:
Z = (Sample Mean - Population Mean) / Standard Error

What is the difference between the two equations? In what scenario is each used? If someone could help elabrote I would appreciate it.

Thanks so much,

Sean