Telephone interviews were conducted on a representative sample of 1,003 adults living in the United States. For this sample, 506 adults admitted that they have paid to download music.

a. Use the survey information to find a point estimate for the true proportion of U.S. adults who have paid to download music.

b. Find an interval estimate for the proportion, part a. Use a 90% confidence interval.

c. Give a practical interpretation of the interval, part b. Your answer should begin with "We are 90% confident...."

d. Explain the meaning of the phrase "90% confident."