National public opinion polls are often based on as few as 1,500 persons in a random sampling of public sentiment on issues of public interest. These surveys are often done in person because the response rate for a mailed survey is very low and telephone interviews tend to reach a larger proportion of older persons than would be represented in the public as a whole. Suppose a random sample of 1,500 registered voters was surveyed about energy issues.

a. If 230 of the 1,500 responded that they would favor drilling for oil in national parks, estimate the proportion of registered voters who would favor drilling for oil in national parks. Use a 95% confidence interval.

b. How many persons must the survey include to have 95% confidence that the sample proportion is within .01 of?

c. A congressman has claimed that over half of all registered voters would support drilling in national parks. Use the survey data to evaluate the congressman's claim. Use a=0.05.