in a minimum of 175 words: Year Gross Federal Debt ($millions) 1945 260,123 1950 256,853

Time series are particularly useful to track variables such as revenues, costs, and profits over time. Time series models help evaluate performance and make predictions. Consider the following and respond in a minimum of 175 words: Year    Gross Federal Debt ($millions) 1945    260,123 1950    256,853 1955    274,366 1960    290,525 1965    322,318 1970    380,921 1975    541,925 1980    909,050 1985    1,817,521 1990    3,206,564 1995    4,921,005 2000    5,686,338