Using the probability of complementary events, it is found that q = 0.25.
<h3>What is a probability?</h3>
A probability is given by the <u>number of desired outcomes divided by the number of total outcomes</u>.
When two events are complementary, the <u>sum of their probabilities is of 1</u>.
For this problem, black balls and white balls are complementary, hence:
p + q = 1.
We have that p = 3q, hence:
3q + q = 1
4q = 1.
q = 1/4
q = 0.25.
More can be learned about probabilities at brainly.com/question/14398287
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