A promotion campaign is being planned to encourage people to reduce heat in their houses at night. In order to measure the campaign's impact, we want to determine the proportion of people who reduce their heat at night. A telephone sample will be taken before and after the campaign.

a. What sample size is required if an accuracy of 0.02 is desired at a 95 percent confidence level?

b. What sample size is required if an accuracy of 0.04 is desired at a 95 percent confidence level?

c. Calculate new sample sizes for part (a) and (b) if you know that the proportion of people who reduce their heat at night would not exceed 0.3.

d. Assume that a before measure was taken with a sample size of 400 and the sample proportion was 0.3. Generate a 90 percent confidence level estimate for the population proportion.