A clock company is concerned about errors in assembly of their custom made clocks. A random sample of 120 clocks from today's production yields nine clocks with assembly errors.
a. Compute the 95% confidence interval for the percentage of clocks with assembly errors in today's production.
b. Interpret this confidence interval.
c. How many clocks should be selected in order to be 95% confident of being within 2% of the population percentage of clocks with assembly errors in today's production?