The customer service manager of Energy Electronics Co., Ltd. is planning to conduct a survey to determine whether customers who purchased a washing machine from his company over the past six months were satisfied with the product. Using the warranty cards submitted by the customers after the purchase over the past six months, the manager made up a list of relevant customers and 220 of them were randomly selected. A questionnaire designed to assess customers' satisfaction with the washing machine was then mailed to each of them.

(a) Describe the population and sample of the survey set up by the manager.

(b) Describe the inference of interest in this survey.

(c) Did the list made up by the manager cover the whole actual population of interest? Explain.