Use the coding of Exercise 15 to rework both parts of Exercise 45.
Exercise 15
When the x's are equally spaced, the calculation of 
and 
can be simplified by coding the x's by assigning them the values ... , -3, -2, -1, 0, 1, 2, 3, ... when n is odd, or the values ... , -5, -3, -1, 1, 3, 5, ... when n is even. Show that with this coding the formulas for and become
Exercise 45
The following data pertain to the chlorine residual in a swimming pool at various times after it has been treated with chemicals:
(a) Fit a least squares line from which we can predict the chlorine residual in terms of the number of hours since the pool has been treated with chemicals.
(b) Use the equation of the least squares line to estimate the chlorine residual in the pool five hours after it has been treated with chemicals.