For Exercises 49–56, do the following:
53. Gas Prices. The American Automobile Association reported in June 2011 that the mean price for a gallon of regular gasoline was $3.70. A recent random sample of 25 gas stations had a mean price of $3.90. Assume normality and . Test, using level of significance , whether the population mean price for a gallon of regular gasoline has risen since June 2011.
9.2.53
(a) (b) . Reject if . (c) .
(d) Since is , the conclusion is reject . There is evidence at the 0.05 level of significance that the population mean price of regular gasoline is greater than $3.70 per gallon. Therefore we can conclude at the 0.05 level of significance that the population mean price for a gallon of regular gasoline has risen since June 2011.