A pharmacist wishes to select three brands of aspirin to sell in his store. He has five major brands to choose from: A, B, C, D and E. If he selects the three brands at random, what is the probability that he will select the following?
(a) brand B
(b) brands B and C
(c) at least one of the two brands B and C

(a) 0.6

(b) 0.3

(c) 0.9

Step-by-step explanation:

We are given that a pharmacist wishes to select three brands of aspirin to sell in his store. He has five major brands to choose from: A, B, C, D and E.

Total number of ways to select 3 brands from total of 5 = = = = 10 .

In all the three parts denominators remains at 10

(a) If he selects the three brands at random, the probability that he will select brand B = one brand B will be selected and other 2 brands will be selected from the remaining 4 brands i.e.

So, required probability = = = 0.6

(b) The probability that he will select the brands B and C = Two brands will be selected of B and C and one brand will be selected from remaining 3 brands i.e.;

So, required probability = = = 0.3 .

(c) The probability that he will select at least one of the two brands B and C    

     = 1 - Probability that neither of the three brands are from B and C

     = 1 - Probability that all three brands are selected from the remaining

              brands of A, D and E

     =  1 - =   = = 0.9 .

the answer is  

d.

21

i did this one. so you should get it right.