http://www.ck12.org Chapter 6. Normal Distribution Curves
6.2 Variance of a Data Set
Here you’ll learn the meaning of variance and calculate the variance for populations and for samples.
Suppose you are a toy maker and you’re testing the efficiency of a new factory process. In the past, the factory was
able to produce an average of 5,500 toys per day. You take a sample of the production runs over a week’s worth of
time. From Monday through Friday here are the production numbers: 6,500; 2,500; 5,700; 8,000; 3,800. How can
you express the differences between the efficiency of this process compared to the previous process? How can you
describe the variance?
Watch This
First watch this video to learn about the variance of normally distributed data.
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Click image to the left for more content.CK-12 Foundation: Chapter6VarianceofNormallyDistributedDataA
Then watch this video to see some examples.
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Click image to the left for more content.CK-12 Foundation: Chapter6VarianceofNormallyDistributedDataB
Watch this video for more help. This video from Khan Academy shows how to calculate the variance and the
6.4 Applications of Variance and Standard Deviation
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Click image to the left for more content.Khan Academy Statistics: Standard Deviation
Guidance
To calculate thevariance(σ^2 )for a population of normally distributed data: