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15. The OLS residuals, a, are defined as follows: a. . Y - Bo - B,X, b. Y, - Bo - BIX c. (Y, - Y)2 d. Y - Y 16. There exist a relationship test scores and the student-teacher ratio can be modeled as a linear function with an intercept of 798.9 and a slope of -3.28. A increase in the student teacher ratio by 2 will: a. Reduces test scores by 3.28 on average b. Results in a test score of 798.9 c. Reduces test scores by 6.56 on average d. Reduces test scores by 6.56 for every school district