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Quadratic Regression
The following table lists the tuition cost per quarter for
taking 15 credits at Green River Community
College since 1980.
Year  Cost  
1980  $102  Year  Cost 
1981  102  1994  $432 
1982  173  1995  450 
1983  173  1996  467 
1984  193  1997  486 
1985  193  1998  505 
1986  233  1999  528 
1987  253  2000  547 
1988  260  2001  581 
1989  274  2002  661 
1990  294  2003  714 
1991  320  2004  771 
1992  333  2005  815 
1993  375  2006  862 
Use your calculator ’s
linear regression function to find a line of best fit for the data. What is
the linear function of best fit? (Hint: It might make things easier if
you use ‘years since 1980’ as
the variable x instead of the year number – so 1980 would be x = 0, and 2006
would be x = 26.)
Use the function you
found in part 1 to estimate the cost of taking 15 credits at GRCC in 2007.
Also estimate the cost in 2010 and 2020.
Plot both the data and
the line on your calculator to see how well it fits. Does it look like a
good fit to you?
Next, use your
calculator to find a quadratic regression for the data. What is the quadratic
function of best fit?
Plot the data and your
quadratic function on your calculator. How well does it fit? Does it look
like it fits better than the line does?
Now use the quadratic
function to try to predict the cost of taking 15 credits at GRCC in 2007,
2010 and 2020.
Do you think the linear function or the quadratic function gives a better prediction? Why?
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