STAT212
In-Class Exercise
Data were collected to investigate the relationship between amount of the restaurant bill and the
amount of the tip. The data are for six dining parties. Using the table below, answer the questions
that follow.
Bill($), x
33.46
50.68
87.92
98.84
63.6
107.34
Tip ($), y
5.5
5
8.08
17
12
16
x2
1119.5716
2568.4624
7729.9264
9769.3456
4044.96
11521.8756
y2
30.25
25
65.2864
289
144
256
xy
184.03
253.4
710.3936
1680.28
763.2
1717.44
a. Construct a scatter plot.
b. Calculate the Pearson correlation coefficient.
c. Determine least squares equation that can be used for predicting a value of y based on a
value of x.
d. Compute  ( y 
yˆ ) 2 for the least squares line.
e. Why do we call the least-squares line the best fitting line?
f. Using your equation in part c, draw the least squares line on the scatterplot you constructed
in part a.
g. If the amount of a bill is $75, predict the amount of the tip that will be left.