Question
A box contains 6 white balls, 5 black balls and 4 red
balls. Two balls are drawn at random without replacement. What is the probability that both balls are of the same colour?Solution
Total balls = 6 + 5 + 4 = 15 Total ways to choose 2 balls = 15C2 = 105 Favourable cases (same colour): White–white: 6C2 = 15 Black–black: 5C2 = 10 Red–red: 4C2 = 6 Total favourable = 15 + 10 + 6 = 31 Probability = 31 / 105.
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