In a sample of 40 days taken at Town Talk Bakery, it was found that an average of 75 cakes per day were sold. From past surveys, the population standard deviation was found to be 25 cakes per day.
a. Determine the standard error of the mean number of cakes sold per day.
b. Determine the 90% confidence interval for the population mean number of cakes sold per day.
c. If you wanted a wider interval, would you increase or decrease the confidence level?