A plant distills liquid air to produce oxygen, nitrogen, and
argon. The percentage of impurity in the oxygen is thought to be
linearly related to the amount of impurities in the air as measured
by the "pollution count" in parts per million (PPM). A sample of
plant operating data is shown in Table 3.
Table 3: A sample plant operating data.
Purity (%), y
93.3
92.0
92.4
91.7
94.0
94.6
93.6
93.1
93.2
Pollution count
(ppm), x
1.10
1.45
1.36
1.59
1.08
0.75
1.20
0.99
0.83
Purity (%), y
92.9
92.2
91.3
90.1
91.6
91.9
Pollution count
(ppm), x
1.22
1.47
1.81
2.03
1.75
1.68
Draw a scatter diagram to illustrate the
above information. (3 marks)
Fit a simple linear regression model and
plot the line on the scatter diagram. (15 marks)
Test the linearity (significance of the
slope) at a 5% significance level. (7 marks)