There are 4 black and 5 white balls in the box. Draw 3 balls at random. What is the probability that 2 of them will turn out to be black?
According to the classical definition of probability, the desired probability is found using the hypergeometric probability formula, so you just need to substitute the original values in the formula.
The urn contains K = 4 black balls and N – K = 5 white (N-total balls).
Substitute in the formula the values: K = 4, N – K = 5. Total, N = 4 + 5 = 9. Choose n = 3 balls, of which there should be 2 black and, accordingly, 3 – 2 = 1 white.
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