Solution — 2019 Question 9 Regression

Using GC, $$r=0.921∎$$

This indicates a strong positive linear correlation between the written test marks and the practical test marks, suggesting that students who score higher in the written test tend to also score higher in the practical test.

Using GC, the equation of the regression line of $y$ on $x$ is $$y=0.112x+1.22∎$$

When $x=22,$

This estimate is reliable because $x=22$ lies within the range of the data $16\le x\le 30,$ and $r=0.921$ indicates a positive linear correlation $∎$