1. Better hiring info. Editors of the business report in Exercise 12 are willing to accept a margin of error of 4% but want 99% confidence. How many randomly selected employers will they need to contact?
2. Pilot study. A state's environmental agency worries that a large percentage of cars may be violating clean air emis- sions standards. The agency hopes to check a sample of ve- hicles in order to estimate that percentage with a margin of error of 3% and 90% confidence. To gauge the size of the problem, the agency first picks 60 cars and finds 9 with faulty emissions systems. How many should be sampled for a full investigation?
3. Another pilot study. During routine conversations, the CEO of a new start-up reports that 22% of adults between the ages of 21 and 39 will purchase her new product. Hearing this, some investors decide to conduct a large-scale study, hoping to estimate the proportion to within 4% with 98% confidence. How many randomly selected adults be- tween the ages of 21 and 39 must they survey?