The Empirical Rule (aka 68-95-99.7 rule) is a way to measure how your data can vary by a few numbers. A bell shape represents all the data with the majority being in the middle. A Z score of "0" runs down the midde of the graph and from each side branches out to Z scores of 1 and 2 (right) and -1 and -2 (left side). From Z scores -1 to 1, represents about 68% of the data. From -2 to 2, it represents about 95% of the data, and from Z scores -3 to 3 represent about 99.7% of your data.
ex) It takes the majority of adults that work downtown 45 minutes to get to work in the morning with a standard deviation of 2.
a) How often do they arive in less than 47 minutes to work?
b) How often does it take more than 49 minutes to get to work?
a: 100% - 16% = 84%
They will arrive to work in less than 47 minutes about 84% of the time
b: 100% - 95% = 5% divided by 2 (tails) = 2.5%
It will take more than 49 minutes to get to work about 2.5% of the time
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