In a Harris poll of 514 human resource professionals, 90% said the appearance of a job applicant is most important for a good first impression.

a. Among the 514 human resource professionals who were surveyed, how many of them said the appearance of a job applicant is most important for a good first impression?

b. Construct a 99% confidence interval estimate of the proportion of all human resource professionals believing the appearance of a job applicant is most important for a good first impression.

c. Repeat part (b) using a confidence level of 80%.

d. Compare the confidence intervals from parts (b), (c) and identify the interval is wider. Why is it wider?