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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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