1. Last year, 23% of sales were by customers that spent more than $500 in my store. I want to repeat the study to see what it is this year. How many sales should I sample if I want to estimate the percent of sales that are more than $500, with a margin of error that is not more than 4% (0.04)? Use 99% confidence.

2. This question will be referred to in several of the next questions: I try 2 marketing approaches and their effect on sales. I have 15 stores that averaged $179,000 in sales (standard dev=$15,000) after marketing approach 1, while trying a different marketing approach after (approach 2) I got $177,000 in sales (standard dev = $9000) for those same stores. I want to find out if they are different.

- What is the standard error (to 1 decimal place)?

- What is the degrees of freedom?

- What is the test statistic (to 2 decimal places)?