The following data show residential and commercial natural gas consumption (quadrillion Btu) from 1992 through 2007.

a. Construct a graph of the time series, then superimpose a three-year centered moving average over the original series.
b. Superimpose a five-year centered moving average over the original series. Why is the moving average €œsmoother€ when N = 5?

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Year Consumption Yer Consumption 1992 1993 1994 1995 1996 1997 1998 1999 29.6 30.6 30.8 33.3 33.0 33.0 32.8 36.0 2000 2001 2002 2003 2004 2005 2006 2007 37.7 37.3 38.2 38.6 38.8 39.6 38.6 40.2