### 9.3 Describing Dispersion

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• Math Help

To confirm the claim in the "Standard Deviation and Dispersion" box that says in any data set, at least 75% of the values lie within 2 standard deviations, at least 89% lie within 3 standard deviations, and at least 94% lie within 4 standard deviations, you can enter the data for Example 1 into a spreadsheet.

Data within 2 standard deviations is between 22 - 2(1) = 20 and 22 + 2(1) = 24.

Data within 3 standard deviations is between 22 - 3(1) = 19 and 22 + 3(1) = 25.

Data within 4 standard deviations is between 22 - 4(1) = 18 and 22 + 4(1) = 26.

So, 41 of the values or about 91% lie within 2 standard deviations of the mean, 45 of the values or 100% lie within 3 standard deviations of the mean, and 45 of the values or 100% lie within 4 standard deviations of the mean.

• Consumer Suggestion

Female sea turtles swim to shore and dig a nest in the sand to lay their eggs. Once the eggs hatch, the young sea turtles emerge at night and must find their way to the ocean. Sea turtles are listed as an endangered species and are protected by organizations and volunteer groups. To find out more about sea turtles and learn how you can help, visit Defenders of Wildlife.

• Checkpoint Solution

Use the data given in the spreadsheet or the Histogram Generator located in Tools to create a histogram.

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