15. SAT Training Course The article “An SAT Coaching Program That Works,” by Kaplan (Chance, Vol. 15, No. 1) included a graph depicting SAT scores for 50 subjects in a control group. Nine of the 50 points were randomly selected, with each point representing the score on the SAT test taken the first time and the score on the SAT test taken a second time, with no preparatory course taken between the two tests. The graph was used to identify the scores listed below. Test the claim that the differences have a mean of 0. What do the results suggest?

Student A B C D E F G H I First SAT score 480 510 530 540 550 560 600 620 660 Second SAT score 460 500 530 520 580 580 560 640 690