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Two balls are selected at random one by one without replacement from a bag containing 4 white and 6 black balls. If the probability that the first selected ball is black, given that the second selected ball is also black, is n m , where gcd (m,n) = 1, then m + n is equal to :

1. 14
2. 4
3. 11
4. 13

Correct answer: 14

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