Polychorinated biphenyls (PCBs) are a group of synthetic oil-like chemicals that were at one time widely used as insulation in electrical equipment and were discharged into rivers. They were discovered to be a health hazard and were banned in the 1970s. Since the, much effort has gone into monitoring PCB concentrations in waterways. Suppose that a random sample of 63 water samples drawn has a sample mean of 1.69 ppb and a sample standard deviation of 0.25 ppb.
A.) Find a 90% confidence interval for PCB concentration.
B.) Find a 95% confidence interval for PCB concentration.
C.) An environmental scientist says that PCB concentration is between 1.65 and 1.73 ppb. With what level of confidence can that statement be made?
D.) Estimate the sample size needed so that a 90% confidence interval will specify the population mean to within ± 0.02 ppb.
E.) Estimate the sample size needed so that a 95% confidence interval will specify the population mean to within ± 0.02 ppb.