According to a government energy agency, the mean monthly household electricity bill in the United States in 2011 was $110.1. Assume the amounts are normally distributed with standard deviation $18.00. Use the TI-84 Plus calculator to answer the following.(a) What proportion of bills are greater than $131?
Question
According to a government energy agency, the mean monthly household electricity bill in the United States in 2011 was 18.00. Use the TI-84 Plus calculator to answer the following.(a) What proportion of bills are greater than $131?
Solution
To solve this problem, we will use the normal distribution function on the TI-84 Plus calculator. Here are the steps:
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First, calculate the z-score for 131, μ = 18.00. So, the z-score is (131 - 110.1) / 18 = 1.16.
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Now, we will use the normalcdf function on the TI-84 Plus to find the proportion of bills greater than $131. To do this, press 2ND, then VARS to access the DISTR menu. Select 2:normalcdf.
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Enter the following values: lower bound = 1.16, upper bound = 1E99 (a very large number to represent infinity), μ = 0, σ = 1. This will calculate the area under the curve from the z-score to positive infinity.
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Press ENTER to calculate. The result is the proportion of bills that are greater than $131.
Remember, the result is a proportion, so if you want to express it as a percentage, you will need to multiply it by 100.
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