The U.S. Energy Information Administration reports weekly figures on retail gasoline prices in Weekly Retail Gasoline and Diesel Prices. Every Monday, retail prices for all three grades of gasoline are collected by telephone from a sample of approximately 900 retail gasoline outlets out of a total of more than 100,000 retail gasoline outlets. For the 900 stations sampled on December 1, 2008, the mean price per gallon for unleaded regular gasoline was $1.811.
a. Is the mean price given here a sample mean or a population mean? Explain your answer.
b. What letter or symbol would you use to designate the mean of $1.811?
c. Is the mean price given here a statistic or a parameter? Explain your answer.