Solve the following:
Q: In a city, 60% of the voters are in favor of building a new park. An interviewer intends to conduct a survey.
a. If the interviewer selects 20 people randomly, what is the probability that more than 15 of them will favor building the park?
b. Instead of choosing 20 people as in part a, suppose that the interviewer wants to conduct the survey until he has found exactly 12 who are in favor of the park. What is the probability that the first 12 people surveyed all favor the park (in which case the interviewer can stop)? What is the probability that the interviewer can stop after interviewing the thirteenth subject? What is the probability that the interviewer can stop after interviewing the eighteenth subject?