There are 20 white and 6 black balls in the urn. A ball is taken out of it at random, after which it is returned

There are 20 white and 6 black balls in the urn. A ball is taken out of it at random, after which it is returned to the urn and all the balls are mixed. Take out one more ball. Find the probability that both balls are black.

In total, there can be 4 options for the development of events (h-black, b-white):
1.h-h
2. h-b
3.b-b
4.b-h
From the diagram, you can easily understand that the probability of the desired outcome is 1/4
Answer: 1/4