Do consumers spend more on a trip to store a or store b? suppose researchers interested in this question collected a systematic sample for 85 store a customers and 82 store b customers by asking customers for their purchase amount as they left the store. using the given summary statistics, researchers calculated a 95% confidence interval for the mean difference between store a and store b purchase amounts. the interval was ($negative 15.96,$negative 4.04). explain in context what this interval means.