An investigation of the relationship between x = traffic flow (thousands of cars per 24 hours) and y 5 lead content of bark on trees near the highway (mg/g dry weight) yielded the accompanying data. A simple linear regression model was fit, and the resulting estimated regression line was y^ = 28.7 1 33.3x. Both residuals and standardized residuals are also given.

a. Plot the (x, residual) pairs. Does the resulting plot suggest that a simple linear regression model is an appropriate choice? Explain your reasoning.
b. Construct a standardized residual plot. Does the plot differ significantly in general appearance from the plot in Part (a)?

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8.3 8.3 12 12. 17.0 227 312 362 52 640 Residual 786.969.6 89.4 45.3 St. resid. -0.99 0.09-0.81 1.04 0.51 17.0 17.0 24.3 24.3 24.3 539 728 945738 759 Residual -55.7 133.3 107.299.8-78.8 St. resid. 0.63 351.250.99