# Thread: Understandable Statistics, Math 201 help.

1. ## Understandable Statistics, Math 201 help.

I am taking a sophomore level class in statistics, and I am not understanding what I am learning and I need help on a homework question. I am not looking for someone to give me the answers outright, but I just need help walking through the problem. Here it is:

Susan is taking Western Civilization this semester on a pass/fail basis. The department teaching the course has a history of passing 71% of the students in Western Civilization each term. Let n = 1, 2, 3, ... represent the number of times a student takes Western Civilization until the first passing grade is received. (Assume the trials are independent.)

(a) Write out a formula for the probability distribution of the random variable n. (Use p and n in your answer.)
P(n) =

(b) What is the probability that Susan passes on the first try (n = 1)? (Use 2 decimal places.)

(c) What is the probability that Susan first passes on the second try (n = 2)? (Use 3 decimal places.)

(d) What is the probability that Susan needs three or more tries to pass Western Civilization? (Use 3 decimal places.)

(e) What is the expected number of attempts at Western Civilization Susan must make to have her (first) pass? Hint: Use μ for the geometric distribution and round.

2. ## Re: Understandable Statistics, Math 201 help.

Originally Posted by ber19
I am taking a sophomore level class in statistics, and I am not understanding what I am learning and I need help on a homework question. I am not looking for someone to give me the answers outright, but I just need help walking through the problem. Here it is:

Susan is taking Western Civilization this semester on a pass/fail basis. The department teaching the course has a history of passing 71% of the students in Western Civilization each term. Let n = 1, 2, 3, ... represent the number of times a student takes Western Civilization until the first passing grade is received. (Assume the trials are independent.)

(a) Write out a formula for the probability distribution of the random variable n. (Use p and n in your answer.)
P(n) =

(b) What is the probability that Susan passes on the first try (n = 1)? (Use 2 decimal places.)

(c) What is the probability that Susan first passes on the second try (n = 2)? (Use 3 decimal places.)

(d) What is the probability that Susan needs three or more tries to pass Western Civilization? (Use 3 decimal places.)

(e) What is the expected number of attempts at Western Civilization Susan must make to have her (first) pass? Hint: Use μ for the geometric distribution and round.
I suggest you review the Geometric Distribution. Your textbook, class notes or Google might be a good start. Note: p = 0.71.