Suppose a consumer advocacy group would like to conduct a survey to find the proportion of the consumers who bought the newest generation of an MP3 player were happy their purchase

a. How large a sample n should they take to estimate p with 2% margin of error and 90% confidence interval.

b. The advocacy group took a random sample of 1000 customers who recently purchased this MP3 player and found that 400 were happy with their purchase. Find a 95% confidence interval for p.