variance and standard deviation

[issa]

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what are the formulas for variance and standard deviation? i found the formulas but they were confusing.

the question: 7 employees with a rating of 5,4,3,3,3,2,1
what is the standard deviation?

i remember that we have to find the avergae and then i don't remember the formula and to do next to solve this problem.

 

[tinman831]

Here's a link that explains it pretty well:

http://www.gcseguide.co.uk/standard_deviation.htm

1) find the average of the numbers.
2) subtract the mean from each number individually and square the result
3) add up all those squared results
4) divide the sum from step 3 by (n-1)
5) square root the result to get your standard deviation

 

[DMD to Be]

Hmm, and this is on the DAT? I haven't see it anywhere in review books...