A class of 50 students obtained the following grades in a st

A class of 50 students obtained the following grades in a statistics course: A 5 B 25 C 15 D 5

If one student is selected at random, what is the probability that a. the student obtained a B?
b. the student obtained either a B or a C?
c. the student did not obtain a D?

d. the student did not obtain either a B or a C?

i get 1/2, 4/5, 9/10, 1/5

Solution

If one student is selected at random, the probability that a. the student obtained a B =25/50 =1/2
b. Probability the student obtained either a B or a C =(25/50)+(15/50) = 40/50 =4/5
c.Probability the student did not obtain a D = 1- (5/50) = 45/50 = 9/10

d. Probability the student did not obtain either a B or a C = 1- (Bor C)=1-(4/5) = 1/5