Question: A power company wants to determine whether or not mean residential electricity usage per slovak household has decreased (due to high daily temperatures) for the Winter 2007. Past experience indicates that the average usage per months is normally distributed with a mean of 700 kwh and a standard deviation of 50 kwh. A simple random sample of 50 households was selected

695, 700, 705, 699, 695, 698, 700, 690, 696, 696, 690, 692, 697, 699, 699, 698, 697, 697, 698, 699, 850, 715, 400, 550, 600, 650, 687, 730, 677, 699, 654, 650, 666, 900, 715, 830,

489, 450, 645, 590, 789, 650, 830, 745, 905, 826, 720, 560, 771, 732.

Test at the 0.05 significance level whether or not the mean residential electricity usage per household has decreased for the Winter 2007.