The following data represent the population of the United States for the years 1900-2010:

An ecologist is interested in finding an equation that describes the population of the United States over time.
(a) Determine the least-squares regression equation, treating year as the explanatory variable.
(b) A normal probability plot of the residuals indicates that the residuals are approximately normally distributed. Test whether a linear relation exists between year and population.
(c) Draw a scatter diagram, treating year as the explanatory variable.
(d) Plot the residuals against the explanatory variable, year.
(e) Does a linear model seem appropriate based on the scatter diagram and residual plot?
(f) What is the moral?