The CEO of a large corporation asks his Human Resource (HR) director to study absenteeism among its executive-level managers at its head office during the year. A random sample of 30 executive-level managers reveals the following:

18 mid-level managers out of the 30 randomly selected mid-level managers, cite stress as a cause of absence.

(a)Construct a 98% confidence interval estimate for the population proportion of mid-level managers who cite stress as a cause of absence.

CI = _____________________________

(b)How many mid-level managers need to be selected to have 99% confidence in estimating population proportion of mid-level managers who cite stress as a cause of absence to within if no previous estimate is available?

_________________________________