Two training classes took a test and the results were marked on the scale zero to one hundred. The first group got an average score of 75, with the standard deviation of 8. The second group got an average of 65, with the standard deviation of 4. How do these two groups compare?
How many in each group?
Z = (mean1 - mean2)/standard error (SE) of difference between means
SEdiff = √(SEmean1^2 + SEmean2^2)
SEm = SD/√n
If only one SD is provided, you can use just that to determine SEdiff.
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z score.