Thirty randomly selected students took the calculus final. If the sample mean was 89 and the standard deviation was 6.2, construct a 99% confidence interval of the mean score of all students. Assume that the population has a normal distribution

For the answer to the question above asking If the sample mean was 89 and the standard deviation was 6.2, construct a 99% confidence interval of the mean score of all students. Assume that the population has a normal distribution

z=2.57 cuts off. 005 in each tail of the standard normal distribution

99% CI is 89 + / - 2.57 (6.2) / sqrt (30) = 89 + / - 2.909, or from 86.09 to 91.91