There are 3 white and 9 black balls in the urn. One ball is taken out of the urn at random. What is the probability that it is black?

To solve this problem, we introduce the conditional variable “X”, through which we denote the probability that the ball taken out of the urn at random turns out to be black.

Then, applying the provisions of the theory of probability and based on the data of the problem, we will compose the following equation: X = 9 / (9 + 3).

Solving this equation, we get X equal to 0.75.

Answer: The probability that a ball taken out of the urn at random turns out to be black is 0.75.