It is generally believed that a practical major such as business or engineering can really pay off for college graduates (CNNMoney.com, July 22, 2010). Other studies have shown that it is not just the major but also how students perform, as measured by their GPA, that influences their salaries. Henry Chen, an employee of PayScale.com, wants to measure the effect of major and GPA on starting salaries of graduates of the University of California at Irvine. He samples starting salaries of five graduates for a given GPA range from the schools of business, engineering, and social sciences. The sample data are shown in the following table.

a. At the 5% significance level, is there interaction between major and GPA?
b. At the 5% significance level, can you conclude that starting salary differs between majors?
c. At the 5% significance level, can you conclude that starting salary depends on GPA?

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Social GPA Business Engineering Sciences 70 3.5-4.0 78 80 62 72 72 48 76 60 48 64 54 3.0-3.5 70 58 64 <3.0 48 52