The emperical rule is also called the 68-95-99.7 rule. This is used on a bell shaped curve graph and you use standard deviation to label locations on the graph. The first line you draw in is the z score and thats down the middle of the graph. Then you have a standard deviation of 1 so theres a line for -1 and 1 and between those values is 68% of your data. With a standard deviation of two it's now 95% of your data and with a standard deviation of three its 99.7% of your data.
Example: It takes you 30 minutes to get to school and the standard deviation is 2 minutes.
Suppose a normal model is appropriate.
A) How often will you get to school less than 32 minutes? Answer : 84%
B) How often will it take more than 34 minutes? Answer: 2.5%
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