Question
A bag contains 6 red, 4 green and 5 blue balls. Two
balls are drawn at random without replacement. What is the probability that both balls are of different colours?Solution
ATQ, Total balls = 6 + 4 + 5 = 15 Total ways to choose 2 = C(15,2) = 105 Same-colour pairs: Red: C(6,2) = 15 Green: C(4,2) = 6 Blue: C(5,2) = 10 Total same-colour = 15 + 6 + 10 = 31 Different-colour = 105 – 31 = 74 Probability = 74/105.
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