Insurance is an important part of family spending. Average car insurance per car is of interest to investigate. A random sample of 25 families are surveyed and we obtain the average car insurance premium is $780 and S.d. is $120 per year. Assume the car insurance premium is normally distributed.
(a) Find a 99% confidence interval for the average car insurance premium and interpret your result.
(b) What is the margin of error when using $780 to estimate the population average car insurance premium with 99% confidence? [Hint: (U-L)/2 ]