Problem
A random sample of 30 customers was selected as part of a study on internet data consumption, and the number of Mega Bytes (MB) was recorded for each customer in the sample for the March 2020. The average usage was found to be 375 MB. In a very large study in the March of the previous year it was found that the standard deviation of the usage was 81 MB. Assuming the standard deviation is unchanged, and that the usage is normally distributed, compute a 90%, 95%, 99% confidence intervals for the mean usage in the March quarter of 2020.