I got the following situation:
2 urns with 2 whites and 3 blacks
2 urns with 1 white and 4 blacks
1 urn with 4 whites and 1 blacks
A ball is drawn from an urn (and this urn is selected at random). The ball is white.
Now, a second ball is drawn from the same urn. What is the probability of getting a black?
ATTEMPT: The urn is selected at random, and we have no further informations about it, so it smells of deception. I think we got to consider only the general set of 10 whites and 15 blacks. So, having independent trials, we calculate $\frac{10}{25} \times \frac{15}{24}$. (Alternatively, using conditional probability formula).
Is this correct?