In this study, we gave 132 high school students fifteen probabilities and nine statistics problems of the Korean College Scholastic Aptitude Test and then analyzed their answer using the classical test theory and the item response theory. Using the classical test theory (the Testian 1.0) we get the item reliability ($0.730 sim 0.765$), and using the item response theory (the Bayesian 1.0) we get the item difficulty ( $-2.32sim0.83$ ) and discrimination ( $0.55sim 2.71$). From results, we find out what and why students could not understand well.