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Question
An urn contains 7 white, 5 black and 3 red balls. Two balls are drawn at random. Find the probability that both the balls are red .
Solution
Out of 15 balls, two balls can be drawn in 15C2 ways.
∴ Total number of elementary events = 15C2 = 105
Out of three red balls, two red balls can be chosen in 3C2 ways.
∴ Favourable number of ways = 3C2 = 3
Hence, required probability = \[\frac{3}{105} = \frac{1}{35}\]
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