College Textbook Sales Narrative
A publisher of college textbooks conducted a study to relate profit per text y to cost of sales x over a six-year period when its sales force (and sales costs) were growing rapidly. These inflation-adjusted data (in thousands of dollars) were collected: Expecting profit per book to rise and then plateau, the publisher fitted the model to the data.
-Refer to College Textbook Sales Narrative. Do the data indicate a significant curvature in the relationship between y and x? Test at the 5% level of significance.

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College Textbook Sales Narrative
A publisher of college textbooks conducted a study to relate profit per text y to cost of sales x over a six-year period when its sales force (and sales costs) were growing rapidly. These inflation-adjusted data (in thousands of dollars) were collected:  Expecting profit per book to rise and then plateau, the publisher fitted the model  to the data.
-Refer to College Textbook Sales Narrative. Do the data indicate a significant curvature in the relationship between y and x? Test at the 5% level of significance.

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The Answer of College Textbook Sales Narrative
A publisher of college textbooks conducted a study to relate profit per text y to cost of sales x over a six-year period when its sales force (and sales costs) were growing rapidly. These inflation-adjusted data (in thousands of dollars) were collected:  Expecting profit per book to rise and then plateau, the publisher fitted the model  to the data.
-Refer to College Textbook Sales Narrative. Do the data indicate a significant curvature in the relationship between y and x? Test at the 5% level of significance.