math
posted by Kristen on .
The breaking strength (in pounds) of a certain new synthetic is normally distributed, with a mean of 172 and a variance of 9. The material is considered defective if the breaking strength is less than 163 pounds. What is the probability that a single, randomly selected piece of material will be defective? (Give the answer to two decimal places.)

Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion related to your calculated Z score.