What is +/- 2 SEM? How would I calculate that? The standard error is 2.786, the standard deviation is 6.229, and the mean is 42.6.

Answer 1

SEM is standard error of the mean. Essentially, if you repeatedly sampled a population you would end up with a group of means for each sampling event. These sample means will vary. So standard error measures how different the sample means are from the population mean. Since you have the standard error calculated already, 2 SEM would be 2 times the standard error and the +/- means your instructor is asking you to calculate the range above (add 2 times the standard error) and below (subtract 2 times the standard error) the mean, which you also have calculated. Statistically this would encompass 95% of the sampled values and produce your 95% confidence interval of the mean.

Good luck!