Refer to the tank temperature–efficiency ratio data given in Exercise 1. a. Determine...

Refer to the tank temperature–efficiency ratio data given in Exercise 1.

a. Determine the equation of the estimated regression line.

b. Calculate a point estimate for true average efficiency ratio when tank temperature is 182.

c. Calculate the values of the residuals from the least squares line for the four observations for which temperature is 182. Why do they not all have the same sign?

d. What proportion of the observed variation in efficiency

Reference exercise 1

The efficiency ratio for a steel specimen immersed in a phosphating tank is the weight of the phosphate coating divided by the metal loss (both in mg/ft²). The article “Statistical Process Control of a Phosphate Coating Line” (Wire J. Intl., May 1997: 78–81) gave the accompanying data on tank temperature (x) and efficiency ratio (y).

a. Construct stem-and-leaf displays of both temperature and efficiency ratio, and comment on interesting features.

b. Is the value of efficiency ratio completely and uniquely determined by tank temperature? Explain your reasoning.

c. Construct a scatter plot of the data. Does it appear that efficiency ratio could be very well predicted by the value of temperature? Explain your reasoning.