Aptitude Day 142

Problems on Probability:

1. A bag contains 3 white, 2 red and 5 blue balls. Three balls are drawn at random from the bag. The probability that all of them are blue is:

Solution:

                 Total Balls = 3+2+5 = 10.

                 n(S) = ¹⁰C₃ = 120.

                 n(E) = ⁵C₃ = 10.

                 P(E) = n(E)/ n(S)

                         = 10/120

                         = 1/12.

2. A bag contains 3 white and 2 red balls. Three balls are drawn at random. What’s the probability that 1 ball is red and the other 2 are white?

Solution:

                  Total Balls = 3+2 = 5

                  n(S) = ⁵C₃ =  10

                  n(E) = ³C₂  *  ²C₁

                          = 3*2

                          = 6.

                 P(E) = n(E)/ n(S)

                         = 6/10

                         = 3/5.