Exercise 4 Page 195

On average, an $\text{increase}$ in time spent playing video games causes a $\text{decrease}$ in time spent learning. At the same time, a $\text{decrease}$ in learning time causes a $\text{decrease}$ in grade point average. By combining the above relations we can say that there is a causation and correlation between time spent playing video games and grade point average. Since an increase in one variable causes decrease in another one, the correlation is negative.