The owner of a sporting goods store surveys a group of customers on (i) the average amount spent, and (ii) whether they purchased at least one item of clothing.

The results of a sample of 80 customers are:

Average amount spent:

Standard deviation:

Number who bought an item of supporter's apparel: 20.

a)Construct a 95% and 99% confidence interval for the mean amount spent per shopper, and interpret your results, commenting on any differences you might observe.