to the U.S. Energy Information Association (eia.gov), the mean electricity consumption per year For a household in the U.S. is 10400 kWh (kWh = kilowatt-hours = kilowatt * hours, it is how you get billed for electricity) with a standard deviation of 2400kWh. Let X = annual electricity consumption, in kWh, of a household and assume
X ~ N(10400, 2400).
1) What percentage of American homes consume between 8000 kWh and 9000 kWh of electricity a year?
Create a new sketch that shows the distribution of X and a shaded region
corresponding to the percentage you find (be sure to label 8000, 9000,and μ on your sketch).
8000 is one standard deviation below the mean of 10400 z-score = .1587
9000 is 1400/2400 =.58 standard deviations below the mean z-score ~~ .2810
.2810 - .1587 = .1223 12 % of households are between 8000 and 9000 kwh consumption
I'll leave the graphing to you.....