If you have a population mean of 50 and a population standard deviation of 5 and you select a sample size of 100, what is the probability that the sample mean is between 47 and 49.5?
Z = (mean1 - mean2)/standard error (SE) of difference between means
SEdiff = √(SEmean1^2 + SEmean2^2)
SEm = SD/√(n-1)
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 related to the Z scores.