There are 3 white and 9 black balls in the urn. 1 ball is taken out of the urn at random

There are 3 white and 9 black balls in the urn. 1 ball is taken out of the urn at random. What is the likelihood that a drawn ball will turn out to be white?

Decision:
The number of all possible results is n = 3 + 9 = 12.
Experiments as a result of which a black ball m = 3 can be taken out.
P = 3/12 = 1/4
Answer: 0.25

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