Operators are to answer telephone calls from customers in an average time of 0.1 minute or less, and either respond to or refer to the proper department within 0.5 minute. Estimate the actual overall time for both components, in total. A pilot study sample of 30 actual operator times was drawn, with the results in following table.

Component Mean time Standard deviation
Answer 0.1023 0.0183
Service 0.5290 0.0902

If the manager wants to be 95 percent confident that the overall time is correctly estimated, with a 3% probability of error, what size sample should be taken?

P bar is .5, alpha is .95, E is .03