As manager for an advertising company, you must plan a campaign designed to increase Twitter usage. You want to first determine the percentage of adults who know what Twitter is. How many adults must you survey in order to be 90% confident that your estimate is within five percentage points of the true population percentage?

a. Assume that nothing is known about the percentage of adults who know what Twitter is.

b. Assume that a recent survey suggests that about 85% of adults know what Twitter is (based on a Pew Research Center survey).

c. Given that the required sample size is relatively small, could you simply survey the adults at the nearest college?