Aptitude Day 144

Problems on Probability:

1. A box contains 5 black and 5 white balls. The probability of drawing 2 balls of the same colour is:

Solution:

                

                Total Balls = 5+5 = 10

                  n(S) = ¹⁰C₂ =  45

                  n(E) = ⁵C₂ + ⁵C₂  = 10+10 = 20

                      

                  P(E) = n(E)/ n(S)

                          = 20/45

                          = 4/9.

2. A box contains 6 red, 7 green and 8 white balls. A ball is drawn at random. What’s the probability that the ball is either white or green?

Solution:

                Total Balls = 6+7+8 = 21.

                  n(S) = ²¹C₁ = 21.

                  n(E) = ⁸C₁ + ⁷C₁  = 8+7 = 15

                      

                  P(E) = n(E)/ n(S)

                          = 15/21

                          = 5/7.