Posted by Donna on .
A population is normally distributed with a man of 100 and a standard deviation of 15. is it unusual for themean of a sample of 3 to be 115 or more? Why or why not?

statistics 
PsyDAG,
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. Essentially it becomes just SEm.
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.
Use that to make you decision.