Linear Regression question 1

Question

I would really be grateful if someone could let me know how to answer Part (a) of Question 1. I believe i should scatter plot both x and y values separately for year 2000 and year 2001 on same graph and prove that there is a change.

am I doing it right or wrong?

2. I am really blank for part c.

Thank you in advance. Will greatly appreciate prompt response.

Answer 1

The scatterplot of the Miles ($X$-axis) vs Faults ($Y$-axis) indicates that

• the number of faults has in most cases decreased in year 2001,
• the two variables (# Faults and line length) are positively related, thus the regression coefficient is positive and probably close to $15/40=3/8$ (since in $x$ we move from $10$ to $50$ and in $y$ from $15$ to $30$).
• the regression line does not seem to pass through the origin (though the validity of this indication should be statistically tested). In contrast, the regression line seems to cross the y-axis somewhere around $10$.