The Federal Reserve reported in its comprehensive Survey of Consumer Finances, released every three years, that the average income of families in the United States increased from 2004 to 2007 after declining from 2001 to 2004. A sample of incomes was taken in 2004 and repeated in 2007. After adjusting for inflation, the data that arise from these samples are given in a file entitled Incomes.

a. Determine if the income of families in the United States in 2004 to 2007 had different standard deviations. Use a significance level of 0.05.

b. Would it be valid to use a two-sample t-test to determine if the average of incomes of U.S.

families was different between 2004 and 2007?

Explain.