According to the record of the registrar's office at a state university, 35% of the students are freshman, 25% are sophomore, 16% are junior, and the rest are senior. Among the freshmen, sophomores, juniors, and seniors, the portion of students who live in the dormitory are, respectively, 80%, 60%, 30%, and 20%. What is the probability that it is a Junior or a senior?

Question

According to the record of the registrar's office at a state university, 35% of the students are freshman, 25% are sophomore, 16% are junior, and the rest are senior. Among the freshmen, sophomores, juniors, and seniors, the portion of students who live in the dormitory are, respectively, 80%, 60%, 30%, and 20%. What is the probability that it is a Junior or a senior?
What formula would I use for this?

Steve · Accepted Answer

total junior or seniors / total students (.16+.24)/1.00 = .40 Those who live in the dorm: (.16*.30 + .24*.20)/1.00 = .096