The breaking strength (in pounds) of a certain new synthetic is normally distributed, with a mean of 173 and a variance of 9. The material is considered defective if the breaking strength is less than 164 pounds. What is the probability that a single, randomly selected piece of material will be defective? (Give the answer to two decimal places.)
Great webpage for this is
http://davidmlane.com/hyperstat/z_table.html
Just enter the mean of 173 , ST of 9
and click on "below" and enter 164
I got .158655
so the prob is appr .16