Based on data from a Harris Interactive survey, 40% of adults say that they prefer to get their news online. Four adults are randomly selected.
a. Use the multiplication rule to find the probability that the first three prefer to get their news online and the fourth prefers a different source. That is, find P(OOOD), where O denotes a preference for online news and D denotes a preference for a news source different from online.
b. Beginning with OOOD, make a complete list of the different possible arrangements of those four letters, then find the probability for each entry in the list.
c. Based on the preceding results, what is the probability of getting exactly three adults who prefer to get their news online and one adult who prefers a different news source.