Question

Our Eco234 course consists of sophomores and juniors. Ten percent of the students who take Econ 234 fail the course. Among those students who pass, 25% are sophomores. 7.5% of the students are juniors who failed the class. Of those who pass, 20% will receive an A for the course. 4. What is the probability that a randomly selected student will be a junior? (10 points) a. .225 b. .25 c. .675 d. .70 e. .75 5. If a student is a sophomore, what is the probability that he/she will pass the class? (10 points) a .12 b .32 c .38 d .40 e. .90 6. Show whether the events "being a sophomore" and "passing the course" are statistically independent. (10 points) 7. What is the probability that a student will not make an A? (10 points)

Answer 1

from above:

	sophomores	Junior	total
pass	0.225	0.675	0.9
fail	0.025	0.075	0.1
total	0.25	0.75	1

4) probability that a randomly selected student will be a junior=0.75

5) probability that he/she will pass the class given sophomore =0.225/0.25 =0.9

6)

as P(pass|sophomore)=P(pass) ; therefore events "being a sophomore" and "passing the course" are statistically independent.

7) probability that a student will not make an A =1-P(make A) =1-0.9*0.2 =0.82