An urn contains 10 white and 5 red balls. If two balls are drawn at random, then what is the probability that <strong>BOTH</strong> the balls are red?

Explanation

The total number of balls is 15. The probability of drawing two red balls is the number of ways to choose 2 red balls out of 5 divided by the number of ways to choose 2 balls out of 15. This is \frac{\binom{5}{2}}{\binom{15}{2}} = \frac{10}{105} = \frac{2}{21}.

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