In: Statistics and Probability
The following data represent a company's yearly sales volume and its advertising expenditure over a period of 8 years.
| 
 Advertising (x)  | 
 Sales (y)  | 
| 
 400,000  | 
 6,000,000  | 
| 
 500,000  | 
 7,200,000  | 
| 
 500,000  | 
 8,000,000  | 
| 
 660,000  | 
 7,500,000  | 
| 
 790,000  | 
 8,900.000  | 
| 
 540,000  | 
 8,100,000  | 
| 
 420,000  | 
 5,900.000  | 
| 
 380,000  | 
 4,000,000  | 
| X | Y | XY | X^2 | Y^2 | 
| 400,000 | 6,000,000 | 2.4E+12 | 1.6E+11 | 3.6E+13 | 
| 500,000 | 7,200,000 | 3.6E+12 | 2.5E+11 | 5.184E+13 | 
| 500,000 | 8,000,000 | 4E+12 | 2.5E+11 | 6.4E+13 | 
| 660,000 | 7,500,000 | 4.95E+12 | 4.36E+11 | 5.625E+13 | 
| 790,000 | 8,900.00 | 7.03E+09 | 6.24E+11 | 79210000 | 
| 540,000 | 8,100,000 | 4.37E+12 | 2.92E+11 | 6.561E+13 | 
| 420,000 | 5,900.00 | 2.48E+09 | 1.76E+11 | 34810000 | 
| 380,000 | 4,000,000 | 1.52E+12 | 1.44E+11 | 1.6E+13 | 

From the above table and formula we get the value are as;
| n | 8 | 
| sum(XY) | 20853509000000 | 
| sum(X) | 4190000.00 | 
| sum(Y) | 40814800.00 | 
| sum(X^2) | 2332100000000.00 | 
| sum(Y^2) | 289700114020000 | 
| b | -3.802980 | 
| a | 7093660.7341 | 
ycap = a + bx
ycap = 7093660.7341 - 3.802980x
when x = 315000
The best predicted sales =
7093660.7341 - 3.802980 * 315000
= 5895722.0
ycap = 7093660.7341 - 3.802980 * 315000
when ycap = 9500000
9500000 = 7093660.7341 - 3.802980 * x
3.802980 * x = 7093660.7341 - 9500000
x = -632751