Why is this solution correct?

What does the answer mean in context of the problem?

According to the Wall Street Journal, 20% of album sales in 2009 were digital. Consider a random selection of 6 album sales. What is the probability that exactly 2 sales were digital?

Solution:

Parameters of the distribution

Number of trials: n=6

Probability of success: p=0.2

Probability of failure: q=0.8

Let x be the number of successes in 6 trials.

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