Originally Posted by

**ThePerfectHacker** Using my software, I found that

$\displaystyle y=-1.83x^2-.29x+30.18$ is and excellent match.

This is not a good predictor of sales from price.

Code:

>x=[14.95;19.95;24.95;29.95]
14.95
19.95
24.95
29.95
>y=-1.838*x^2-0.29*x+30.18
-384.953
-707.134
-1121.22
-1627.2
>
>
>x|y
14.95 -384.953
19.95 -707.134
24.95 -1121.22
29.95 -1627.2
>

A better model can be obtained using the Excel Solver, this gives

a solution:

$\displaystyle

sales=1650.22+195.16\ price - 7.999\ price^2

$

This gives:

Code:

>
>price=[14.95;19.95;24.95;29.95]
14.95
19.95
24.95
29.95
>sales=-7.999*price^2+195.16*price+1650.22
2780.07
2360.04
1540.06
320.139
>
>
>price|sales
14.95 2780.07
19.95 2360.04
24.95 1540.06
29.95 320.139
>

A plot comparing this model with the estimated sales is shown in the attachment

RonL