Question

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 of a particular type is normally distributed with mean value 1000 and standard deviation 150.

(a) How likely is it that a single randomly selected specimen will have a permeability index between 850 and 1300? (Round your answer to four decimal places.)
P(850 < x < 1300) =  

(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 average permeability index will be as follows?

(i) between 900 and 1200 (Round your answer to four decimal places.)
P(900 < x < 1200) =  

(ii) between 850 and 1300 (Round your answer to four decimal places.)
P(850 < x < 1300) =

You may need to use the appropriate table in Appendix A to answer this question.

Answer 1