The prerequisite for a required course is that students must have taken either course a or course b. by the time they are juniors, 51% of the students have taken course a, 25 % have had course b, and 12% have done both. a) what percent of the juniors are ineligible for the course? b) what's the probability that a junior who has taken course a has also taken course b? c) are taking these two courses disjoint events? explain. d) are taking these two courses independent events? explain.