Research suggests that the electrical conductivity (EC) of soil is related to plant growth. Nutrients in the soil are in the form of ions. These ions in the soil become dissolved in water and carry an...

Research suggests that the electrical conductivity (EC) of soil is related to plant growth. Nutrients in the soil are in the form of ions. These ions in the soil become dissolved in water and carry an electrical charge, and this determines the soil EC. Too little EC indicates a lack of nutrients, and a high EC level suggests a salinity problem. A random sample of corn fields in Iowa was obtained and the soil EC was measured in each (x, in mS/cm). The resulting crop yield was also recorded (y, in bushels per acre). The data are given in the following table.

a. Find the estimated regression line.

 b. Conduct an F test for a significant regression (a = 0.05). Explain your results in the context of this problem. Find bounds on the p value associated with this test. Use technology to verify your answer.

 c. Carefully sketch a normal probability plot of the residuals and a plot of the residuals versus the predictor variable. Do these graphs provide any evidence that the simple linear regression assumptions are invalid? Justify your answer.