The U. S. Energy Information Administration surveys households to obtain data on residential energy consumption and expenditures and find out the mean residential energy expenditure of all U. S. families in 1995 was $1,123. That same year, 15 randomly selected upper-income families reported their energy expenditures. Their mean energy expenditures was $1,344.27 and the standard deviation was $231.
At the 5% significance level, do the data indicate that in 1995, upper-income families spent more on the average, for energy than the national average of $1,123?