statistics
posted by Michael .
If the ages of colleges students are normally distributed with a mean of 27 years and a standard deviation of 3.4, what is the probability that a sample of 34 students would have an average age of at least 25.6 years

Z = (mean1  mean2)/standard error (SE) of difference between means
SEdiff = √(SEmean1^2 + SEmean2^2)
SEm = SD/√(n1)
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 that Z score.