It is proposed that fuel efficiency (Y km/l) in motorway test conditions can be well modelled by a linear relationship with engine size (X litres). Eight cars drive a motorway test route and their engine size and fuel efficiency are recorded in the table below. The linear regression model can be written as

Y=?0+?1X+?

(1) Create sketches of scatter plots for the situations when:

(a) The correlation coefficient is 0. (b) The correlation coefficient is -0.8.

(2) Calculate and interpret a 90% confidence interval for?1.

\f