The file S02_27.xlsx contains monthly data for total U.S. retail sales of building materials. There are really two series, one of actual values and one of seasonally adjusted values. The latter adjusts for any possible seasonality, such as higher values in June and lower values in January, so that any trends are more apparent.
a. Is there an observable trend in these data? That is, do the values of the series tend to increase or decrease over time?
b. Is there a seasonal pattern in these data? If so, what is the seasonal pattern?