The monthly commercial and residential prices for natural gas (dollars per thousand cubic feet) in the United States from January 2008 through December 2014 are stored in Natural Gas. (Data extracted from Energy Information Administration, U.S. Department of Energy, www.eia.gov, Natural Gas Monthly, March 1, 2015.)

For the commercial price and the residential price,

a. do you think the price for natural gas has a seasonal component?

b. plot the time series. Does this chart support your answer in (a)?

c. compute an exponential trend forecasting equation for monthly data.

d. interpret the monthly compound growth rate.

e. interpret the monthly multipliers. Do the multipliers support your answers in (a) and (b)?

f. compare the results for the commercial prices and the residential prices.