A researcher finds that 15 percent 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 is the number of people surveyed, since each person is one trial with two possible outcomes: takes the train or does not. The researcher polls 250 people, so there are 250 trials. The 15 percent is the probability of success, not the number of trials.

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