10. When events are independent, the joint probability is the product of the individual probabilities.
... p(senior & female) = p(senior) × p(female) = 0.30 × 0.54 = 0.162 = 16.2%
11. When events are mutually exclusive, the probability of one or another is the sum of the individual probabilities.
... p(soph or frosh) = p(soph) + p(frosh) = 0.28 + 0.26 = 0.54 = 54%