Chapter 8, Problem 35CR

Water permeability of concrete can be measured by letting water flow across the surface and determining the amount lost (in inches per hour). Suppose that the permeability index x for a randomly selected concrete specimen is normally distributed with mean value 1000 and standard deviation 150.

1. a. How likely is it that a single randomly selected specimen will have a permeability index between 850 and 1300?
2. b. If the permeability index is to be determined for each specimen in a random sample of size 10, how likely is it that the sample mean permeability index will be
   1. i. between 950 and 1100?
   2. ii. between 850 and 1300?