A university plans on conducting a survey of its recent graduates to determine information on their yearly salaries. It randomly selected 200 recent graduates and sent them questionnaires dealing with their present jobs. Of these 200, however, only 86 were returned. Suppose that the average of the yearly salaries reported was $75,000.
(a) Would the university be correct in thinking that $75,000 was a good approximation to the average salary level of all of its graduates? Explain the reasoning behind your answer.
(b) If your answer to part (a) is no, can you think of any set of conditions relating to the group that returned questionnaires for which it would be a good approximation?