Aptitude Day 141

Problems on Probability:

1. A bag contains 5 red and 4 white balls. One ball is drawn at random. What’s the probability that the ball drawn is red?

Solution:

                n(S) = 5+4 = 9.

                P(E) = n(E)/ n(S)

                         = 5/9.

2. A box contains 6 green, 5 yellow and 4 white balls. Three balls are drawn at random. What’s the probability that they are not the same colour?

Solution:

                Total balls = 6+5+4 = 15.

                n(S) = ¹⁵C3 = 455.

                n(E) = Event of getting the same colour = ⁶C₃ + ⁵C₃ + ⁴C₃

                                                                                 = 20+ 10+ 4 = 34.

               Probability of getting the same colour, P(E) = n(E)/ n(S)

                                                                                      = 34/455.

              The required probability = 1 – P(E)

                                                      = 1- 34/455

                                                      = 421/455.