The number of pounds of steam used per month by a chemical plant is thought to be related to the average ambient temperature (in°F) for that month. The past year’s usage and temperature are shown in...

The number of pounds of steam used per month by a chemical plant is thought to be related to the average ambient temperature (in°F) for that month. The past year’s usage and temperature are shown in the following table:

presents data on
y
= steam usage and
x
= average monthly temperature.

(a) What proportion of total variability is accounted for by the simple linear regression model?

(b) Prepare a normal probability plot of the residuals and interpret this graph.

(c) Plot residuals versus
and
x. Do the regression assumptions appear to be satisfied?