Help with probability

North Carolina State University posts the grade distributions for its courses online. Students in Statistics 101 in the Fall 2007 semester received 26% A's, 42% B's, 20% C's, 10% D's, and 2% F's. Choose a Statistics 101 student at random. To "choose at random" means to give every student the same chance to be chosen. The student's grade on a four-point scale (with A = 4) is a discrete random variable X with this probability distribution:

Value of X (Probability) 0 (0.02) 1 ( 0.10) 2 (0.20) 3 (0.42) 4(0.26)


The probability of each of each value of X is in parentheses

(a) What values of random variable X are represented by the event "the student got a grade poorer than C"? Write your answer as a comma-separated list.


(b) What is the probability of the event from part (a)?

a) You need lower than C so you can only use the first 2.
0(.02) + 1(.1) = .1

b) P = (.02 + .1) = .12

For part (a):

The values of the random variable X for a grade lower than C is:

0 (0.02) + 1 ( 0.10) + 2 (0.20) =

FOR PART B

P = Probability)
P(grade lower than C) = P(.02+.10+.20) = .32 or 32%