A researcher finds that 15% of all commuters in a metropolitan area take the train to work. The researcher polls 250 people in the area and asks them whether they take the train to work. What is the number of trials for this binomial experiment?

The number of trials in a binomial experiment is the number of people included in the poll. Since the researcher asks 250 people, there are 250 trials. The 15% describes the probability of success on each trial; it does not change the number of trials.

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