(Choose1answer)
The compressive strength of concrete is normally distributed with mean = 1200 psi and standard deviation=30.A random sample of n=9 specimens will have a sample mean diameter that falls in the interval from 1011 psi to 1230 psi. What is the standard error of the sample mean?
A. 400/3
B. None of the others
C. 40
D. 30/9
E. 10
Exit 15
