A researcher wishes to estimate, with 90% confidence, the percentage of adults who support abolishing the penny. His estimate must be accurate within 4% of the true proportion.
(a) Find the minimum sample size needed, using a prior study that found that 25% of the respondents said they support abolishing the penny. (Round to the nearest whole number)
(b) No preliminary estimate is available. Find the minimum sample size needed.(Round to the nearest whole number)