Aptitude Day 145

Problems on Probability:

1. In a class, there are 20 boys and 10 girls. Three students are selected at random. The probability that 1 boy and 2 girls are selected is:

Solution:  

                Total Balls = 20+10 = 30

                  n(S) = ³⁰C₃ =  4060.

                  n(E) = ²⁰C₁ * ¹⁰C₂  = 20+45 = 900

                      

                  P(E) = n(E)/ n(S)

                          = 900/4060

                          = 45/203.

2. Three persons are chosen at random from a group of 4 men, 3 women and 2 children. The chance that exactly 2 of them are children is:

Solution:

                Total Balls = 4+3+2 = 9

                  n(S) = ⁹C₃ =  84

                  n(E) = ⁷C₁ * ²C₂  = 7*1 = 7

                      

                  P(E) = n(E)/ n(S)

                          = 7/84

                          = 1/12.