Electricity bills: According to a government energy agency, the mean monthly household electricity bill in the United States in 2011 was $110.82. Assume the amounts are normally distributed with standard deviation $20.00. Use the TI-84 Plus calculator to answer the following. (a) What proportion of bills are greater than $126? (b) What proportion of bills are between $83 and $137? (c) What is the probability that a randomly selected household had a monthly bill less than $112? Round the answers to at least four decimal places.

Features Features Normal distribution is characterized by two parameters, mean (µ) and standard deviation (σ). When graphed, the mean represents the center of the bell curve and the graph is perfectly symmetric about the center. The mean, median, and mode are all equal for a normal distribution. The standard deviation measures the data's spread from the center. The higher the standard deviation, the more the data is spread out and the flatter the bell curve looks. Variance is another commonly used measure of the spread of the distribution and is equal to the square of the standard deviation.