statistics

A researcher wishes to estimate, with 95% confidence, the population proportion of adults who are confident with their country’s banking system. His estimate must be accurate within 2% of the population proportion.
(a) No preliminary estimate is available. Find the minimum sample size needed.
(b) Find the minimum sample size needed, using a prior study that found that 24% of the respondents said they are confident with their country’s banking system.
(c) Compare the results from parts (a) and (b).

Part A:
What is the minimum sample size needed assuming that no prior information is available?

n = _____ (Round up to the nearest whole number as needed.)

Part B: What is the minimum sample size needed using a prior study that found that 24% of the respondents said they are confident with their country’s banking system?

n = _____ (Round up to the nearest whole number as needed.)

Part C:
How do the results from (a) and (b) compare? Pick the best choice:
Choice A: Having an estimate of the population proportion raises the minimum sample size needed.
Choice B: Having an estimate of the population proportion reduces the minimum sample size needed.
Choice C: Having an estimate of the population proportion has no effect on the minimum sample size needed.