According to the U.S. Energy Information Administration, a heating degree-day is a relative measurement of outdoor temperature that indicates how far the average daily temperature is below 65° Fahrenheit. The higher the number of heating degree-days, the greater the national demand for heating energy from sources like natural gas and electricity. The following monthly data show the number of heating degree-days from 1992 through 1995.

a. Construct a graph of the time series. Does the overall trend appear to be upward or downward?
b. Determine the three-month and five-month centered moving average curves and superimpose each on the original time series.

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м 1992 1993 1994 1995 852 860 1031 826 603 152 345 368 644 827 46 128 864 38 21 813 594 543 293 174 366 767 168 46 F. 1992 1993 301 822 824 723 862 14 24 74 564 11 302 89 1994 1995 268 239 580 479 598 16 65 13 11 97