1. Over the past year, an audio store has sold stereo systems produced by three different manufacturers. Of the 400 units from company A, 12% were returned for service during the warranty period. This compares to 15% of 300 units from company B, and 16% of 500 from company C. Assuming that the store's sales are a representative sample of the stereo systems produced by the three manufacturers, use the 0.025 level of signifi- cance in testing whether the population percentages of warranty service returns could be equal.
2. Union members in a large firm work in three departments: assembly, maintenance, and shipping/ receiving. Twenty of a random sample of 30 assembly workers say they intend to ratify the new contract negoti- ated by union leaders and management. This compares to 30 of 40 maintenance workers and 25 of 50 shipping/ receiving workers who say they will ratify the contract. At the 0.025 level of significance, test the null hypothesis that the population proportions are the same for all three departments.