A student’s AP statistics project involves comparing the time it takes a student to complete a set of 25 basic trinomial factoring problems while listening to either rap music or country music. Twelve students are timed on two different sets of problems of equal difficulty. The order of which set of problems he does first and which music he listens to first are randomized. The resulting data is thus paired, with each student acting as his own "pair." Which of the following conditions is required to perform a t-test on these paired data? A. The distribution of times for all students on each set of problems must be approximately Normal.
B. The distribution of times for all students while listening to each type of music must be approximately Normal.
C. The distribution of times for all 24 sets of problems (12 students are taking 2 tests each) must be approximately Normal.
D. The distribution of differences between each individual student’s times on each of the two tests (time with rap – time with country) must be approximately Normal.