Nine students took the SAT. Their scores are listed below. Later on they took a test ...

Nine students took the SAT. Their scores are listed below. Later on they took a test preparation course and retook the SAT. Their new scores are listed below. Construct a 95% confidence interval for ud - means difference. Assume that the distribution is normally distributed.
 

student 1 2 3 4 5 6 7 8 9
before 720 860 850 880 860 710 850 1200 950
740 860 840 920 890 720 840 1240 970