The U.S. Energy Information Administration (US EIA) reported that the average price for a gallon of regular gasoline is $3.94 (US EIA website, April 6, 2012). The US EIA updates its estimates of average gas prices on a weekly basis. Assume the standard deviation is $.25 for the price of a gallon of regular gasoline and recommend the appropriate sample size for the US EIA to use if they wish to report each of the following margins of error at 95% confidence.

a. The desired margin of error is $.10.

b. The desired margin of error is $.07.

c. The desired margin of error is $.05.