Question: It is contract negotiation time, and the Louisiana teachers union wants to argue that its salaries are the lowest in the region. Because the union has 20,000 members, it must rely on a survey. If the union wants to estimate its members' mean salary and be 95% sure that the estimate is within $200 of the real mean, how large a sample should the union use? Assume that a preliminary survey estimates the mean as $15,000, with a $1,000 standard deviation.