A consumer-research organization routinely selects several car models each year and evaluates their
fuel efficiency. In this year’s study of two similar subcompact models from two different automakers,
the average gas mileage for 12 cars of brand A was 27.2 miles per gallon, and the standard deviation
was 3.8 mpg. The nine brand B cars that were tested averaged 32.4 mpg, and the standard deviation
was 4.3 mpg. At a = 0.01, should it conclude that brand A cars have lower average gas mileage than
do brand B cars?