Question

A classroom has ten students. Three students are freshman, two are sophomores, and five are juniors. Three students are randomly selected (without replacement) to participate in a survey. Consider the following events: A = Exactly 1 of the three selected is a freshman B = Exactly 2 of the three selected are juniors Find the following probability. If needed, round to FOUR decimal places. Pr(A∩B) = ___________

Answer 1

To find the probability that exactly one freshman and exactly two juniors are selected, we calculate the combination of selecting one from three freshmen and two from five juniors, then divide by the total combinations of selecting three students from ten. The probability is 0.25.

Step-by-step explanation:

We need to find the probability Pr(A∩B) where:

• A is the event that exactly 1 of the three selected is a freshman.
• B is the event that exactly 2 of the three selected are juniors.

For both events A and B to occur simultaneously, we must select one freshman and two juniors in our three student picks. The number of ways to choose one freshman out of three is C(3,1), and the number of ways to choose two juniors out of five is C(5,2). The total number of ways to choose any three students out of ten is C(10,3). Hence, the probability is:

Pr(A∩B) = (C(3,1) × C(5,2)) / C(10,3)

Calculating this gives:

Pr(A∩B) = (3 × 10) / 120 = 30 / 120

Pr(A∩B) = 0.25

Answer 2

0.25

Step-by-step explanation:

We have a total of ten student, and three students are randomly selected (without replacement) to participate in a survey. So, the total number of subsets of size 3 is given by 10C3=120.

On the other hand A=Exactly 1 of the three selected is a freshman. We have that three students are freshman in the classroom, we can form 3C1 different subsets of size 1 with the three freshman; besides B=Exactly 2 of the three selected are juniors, and five are juniors in the classroom. We can form 5C2 different subsets of size 2 with the five juniors. By the multiplication rule the number of different subsets of size 3 with exactly 1 freshman and 2 juniors is given by

(3C1)(5C2)=(3)(10)=30 and

Pr(A∩B)=30/120=0.25