The Department of Labor would like to estimate the average weekly wages for U. S. adults with a margin of error equal to $ 20. Determine the sample sizes needed to construct a confidence interval for this estimate using the following confidence levels. Assume the population standard deviation for the weekly wage is $ 160.
a. 90%
b. 95%
c. 98%
d. Explain why the confidence level affects the sample size needed to obtain a particular margin of error.