Part A

A supermarket has checked the expenditures of 50 customers on one day and found the average total spent is $75.58. If you can assume that the standard deviation of expenditure for all customers is $28.50 find a 95% confidence interval for the average amount spent by all customers on this day.

Part B

Isabella is a retailer who wants to test a theory about retail turnover in NSW. She downloads NSW estimated resident population data (in thousands) for each quarter from March 1990 to December 2015 and the corresponding seasonally adjusted retail turnover figures for NSW (in $million) from the Australian Bureau of Statistics (Australian Economic Indicators, July 2016 and Australian Demographic Statistics, June 2016) and runs a regression analysis. The output for this is shown below.

B0 = -29215.132

B1 = 6.66

In a way that Isabella's staff could understand, interpret this equation to explain the estimated retail expenditure in September quarter 2012 when there were 7,000,707 residents of NSW, and the rate of increase thereafter.