In a Test of Physical Fitness, a Group of Men $\mu$

Essay

In a test of physical fitness, a group of men ages 65 and older from a local retirement community were told to do as many sit-ups as they could.It is known the population mean $\mu$ is 20 with $\sigma_{X}=8$ The scores for the men from the retirement community are given below.Use a two-tailed rejection region with a total area of 0.05.What is the standard error of the mean?