Can the sample standard deviations s1 and s2 be used in place of the population standard deviations σ1 and σ2?

1. "Testing the Difference between Two Means." (Note: Please respond to only one of the following two bulleted items)

What two assumptions must be met when you are using the z test to test differences between two means?

2. Use the Internet to research an annual report of a retail company.

Then, imagine you are an investor or creditor; suggest the ratios that you believe would provide an investor or creditor with the most important information needed to make accurate predictions about the company's financial condition. When analyzing a company, is it more important to compare the ratios to competitors or to the company's previous history?