PFOA is chemical employed in products that coat cookware to prevent food from sticking. An agency is investigating potential risk of PFOA as a cancer-causing agent. It is known that the blood concentration of PFOA in the general population has a mean of 6ppb and a standard deviation of 10ppb.
An article reported on tests for PFOA exposure conducted on a sample of 323 people who live near a factory that makes one such non-stick cookware product.
If this sample comes from a population of 1461 what is the probability that the average blood concentration of PFOA in the sample is greater than 7.5ppb?