A company is concerned about the level of customer satisfaction with the service provided by its domestic and overseas call center operations. A random sample of customers calling its domestic call center showed that 267 out of 400 were satisfied or very satisfied with the service. A random sample of customers calling its overseas call center showed that 350 out of 500 were satisfied or very satisfied with the service.
(a) Explain what is meant by a 90% confidence interval for a sample proportion.
(b) Test whether there is a difference in the proportion of customers satisfied or very satisfied with the service provided at the two call centers.