An article in Wear (Vol. 152, 1992, pp. 171€“181) presents data on the fretting wear of mild steel and oil viscosity. Representative data follow, with x = oil viscosity and y = wear ear volume (10 €“4 cubic millimeters).




(a) Construct a scatter plot of the data. Does a simple linear regression model appear to be plausible?
(b) Fit the simple linear regression model using least squares. Find an estimate of σ2.
(c) Predict fretting wear when viscosity x = 30. (d) Obtain the fitted value of y when x = 22.0 and calculate the corresponding residual.

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240 181 193 155 172 9.4 15.5 20.0 22.0 1.6 113 75 94 110 33.0 35.5 43.0 40.5