You plan to develop a new iOS social gaming app that you believe will surpass the success of Angry Birds and Facebook combined. In forecasting revenue, you need to estimate the percentage of all smartphone and tablet devices that use the iOS operating system versus Android and other operating systems. How many smartphones and tablets must be surveyed in order to be 99% confident that your estimate is in error by no more than two percentage points?
a. Assume that nothing is known about the percentage of portable devices using the iOS operating system.
b. Assume that a recent survey suggests that about 43% of smartphone and tablets are using the iOS operating system (based on data from NetMarketShare).
c. Does the additional survey information from part (b) have much of an effect on the sample size that is required?