Refer to Exercise 1.

a. Find a 95% confidence interval for the coefficient of Oxygen.

b. Find a 99% confidence interval for the coefficient of Nitrogen.

c. Find a 98% confidence interval for the coefficient of the interaction term Oxygen ? Nitrogen.

d. Can you conclude that β₁

e. Can you conclude that β₂ > ??1000? Find the P-value.

Refer to Exercise 1.

The article ??Advances in Oxygen Equivalence Equations for Predicting the Properties of Titanium Welds??(D. Harwig, W. Ittiwattana, and H. Castner, The Welding Journal, 2001:126s??136s) reports an experiment to predictvarious properties of titanium welds. Among other properties, the elongation (in %) was measured, along with the oxygen content and nitrogen content (both in percent). The following MINITAB output presents results of fitting the model Elongation = β₀ + β₁ Oxygen + β₂ Nitrogen + β₃ Oxygen ? Nitrogen

The regression equation is Elongation 46.80 - 130.11 Oxygen - 807.1 Nitrogen + 3580.5 0xy*Nit SE Coef 3.702 20.467 158.03 Predictor Constant Oxygen Nitrogen Oxy+Nit Coef 46.802 - 130.11 -807.10 3580.5 12.64 -6.36 -5.107 3.737 P 0.000 0.000 0.000 0.001 958.05 S = 2.809 R-Sq = 74.5% R-Sq(adj) = 72.3%